Re-Throating Texans for Better Chambering and Accuracy

I posted on GTA but for those of you who only do AGN here's my Texan mod.

The chamber of AirForce Texan rifles is too short.
For other DIYers here’s some detailed explanations how I fixed that.

Most bullets barely enter the barrel by finger force and since there is no bolt handle and/or probe to act as a force multiplier to help engrave the bullet into the rifling like on other styles of airgun you push in till it hurts your finger tips... and that’s just not good enough.
And so a great deal of the bullet usually hangs out into the ‘loading tray’ of the barrel. Hard to get consistency that way and consistency is the biggest key to accuracy.

This adversely effects accuracy because the bullet frequently ends up slightly cocked (usually the tail of the bullet is raised slightly in my experience) and when launched/fired it is swagged down into the rifling lopsided. Who cares if your only shooting 50 yards but if your shooting for precision or long range it MAKES A DIFFERENCE.

On both rifles I used a variety of bullets (I most commonly shoot) to test the depth they could be inserted with finger pressure and determined that the .257 needed 0.175 deeper and the .457 needed 0.200 deeper (see Pics of bullets in the chamber, before and after on the .257).
Note: I started out with the criteria of at least one caliber of bore contact as a minimum length to ensure a ‘squarely aligned’ bullet in the bore. Since most of the slugs I fire are fairly heavy/long the actual depth I would be cutting would be more than that which was even better. I wanted most of the bullet(s) to be in the bore for my rifles.

So I decided to make the chamber longer on both my .257 and .457 Texans.
I used throating reamers from:
https://www.reamerrentals.com/SearchResults.asp?Cat=25

I ordered them online and USPS delivered them in a Flat Rate box in two days. You get them for three business days but you can pay extra and get them for 14 days if you need. I also got the ‘insurance’ in case I accidentally chipped or broke one although with my experience it was unlikely. I expected the job to be done in one day and only take an hour total for both guns… and that included pulling the barrels out of the guns so did not need more days. It took 10 times longer to write this up than to do the job on both rifles combined.

Technically a cautious person could manually hand ream their chamber with a tap wrench T-handle, the reamer ends are 3/8” square ended. I would NOT use a crescent wrench for this as it would put side force on the reamer and cut the barrel wrong or even break the reamer!!! Use of a T wrench keeps the side forces minimized. You just have to take TINY bites as you feed forward and watch how deep you go… stopping a couple of times to extract the reamer, clean out the chips in the bore and test fit your bullet till it goes as deep as you want. Of course you would want to keep it VERY straight with no side force but the reamers are live piloted and do a pretty good job all by themselves. You would find that it cuts the rifling out so easy it only needs thumb n fingers on the T-wrench and a light to medium forward pressure, not a gorilla grip pushing and turning the reamer.
LOTS of lubricant in the barrel and on the tap is NECESSARY! I use TapMagic myself.

I however, have a small lathe, so used that to center everything (like a jig) instead of doing it manually. BUT, I NEVER TURNED IT ON!

First I GENTLY test fit by hand the reamer into the barrel, rotating with my fingers as I slid it in deeper to see when the reamer would touch the existing rifling lead in the barrel. I then measured with a caliper (from the end of the barrel to the ends of the flutes on the reamer) that to establish a datum point. Yes I might be off .002 or even as much as .005 but in this case the exact depth of the chamber extended is not THAT critical like headspacing a powder burner chamber. The depth I’m extending the throat is not based on only one bullets exact chambering need but is an average of different bullets length/profile for ‘best fit for all’… so I figure there is a +- of 0.010 anyway for ‘good enough’. Its why it could be done by hand too, not that much depth precision needed.

With the gears set to neutral on the headstock - I put the barrel into the 3jaw chuck and instead of using a live center in the tailstock, just used a drill chuck. The intent was to hold the reamer non-rotating and I would turn the chuck holding the barrel by hand, SLOWLY feeding the tailstock forward a few thousands at a time.

NOTE: In this procedure DO NOT feed the reamer forward with the tailstock screw unless the chuck holding the barrel is turning or you will break the reamer! (Also, don't turn a reamer backwards without pulling it back out of contact as it dulls the cutting edges, or could chip them)

I ran the reamer in till the datum distance I’d measured earlier was close, then with my left hand started turning the chuck about one revolution every 15 seconds and while SIMULTANEOUSLY, SLOWLY feeding the tailstock forward at about a .01 at a time with my right hand. If you can't use both hands at the same time then have some one else do it for you!

In a minute I could feel the reamer was taking a bite with just a bit of drag turning the lathe chuck with my hand. You are not boring the whole barrel, just taking out some of the raised rifling so it does not take much to do that.
I fed the tailstock forward about 90% of the depth I’d determined and pulled the reamer back, blew out the chips in the barrel and test fit a bullet in till it touched the new lead distance. I saw that I was very close to the desired seating depth so used a cleaning rod to bump the bullet back out and reinserted the reamer forward… BEING VERY CAREFUL to approach the cutting depth slowly again so I did not take a huge bite and ruin the barrel or chip the reamer cutting edges. It only took me one test fit on the .257 barrel but it took two test fits on the .457 to get the ‘perfect’ depth I wanted.
Doing this the maxims of “Haste makes waste” or “Measure twice, cut once” are good to follow for a successful/satisfactory job.

I am NOT a photographer, just using my cell phone camera and resizing to fit the forum so I did the best I could with these photos.

First, here's the .457 reamer

1571089881_11490948215da4edd96b5844.62908478_1r 457 Throating reamer.jpg


.457 Lead before throating

1571089899_16355819665da4edeb27ab33.67824676_2r Before 457 lead_726.jpg


.457 Lead after throating 0.200 deeper (the photo is foreshortened so it does not look that much deeper)

Note also that there is not a ridge, the taper just is shadowed in the pic.

1571089909_9698145995da4edf5a92ab4.85071379_3r After 457 lead_947.jpg


Before and after of my 327gr BTHP

1571089920_10075717395da4ee00b44469.99223978_4r Before 327gr BTHP_825.jpg


1571089932_884243465da4ee0c012dc0.84479790_5r After 327gr BTHP_030.jpg


Before and after of the NSA 154gr

1571089943_22448405da4ee17d7e613.77959364_6r Before NSA 154gr BTHP_024.jpg


1571089954_10704317655da4ee22a8eb07.08338353_7r After NSA 154gr BTHP_709.jpg


Before and after of the NSA 290gr FBHP

1571089963_6216255775da4ee2b628ab1.25789544_8r Before NSA 290gr FBHP_117.jpg


1571089976_1596025505da4ee3833f0a3.70124072_9r After NSA 290gr FBHP_417.jpg


Before and after of the NSA 372gr cast Spitzer

1571089994_1878539875da4ee4a3a0711.54497657_10r Before NSA 372gr cast Spitzer_213.jpg


1571090013_1728783985da4ee5df04e69.75782622_11r After NSA 372gr cast Spitzer_256_1.jpg


Before and after of the NSA 350gr BTHP

1571090028_15650304285da4ee6caf92a2.01737387_12r Before NSA 350gr BTHP_924.jpg


1571090056_4234049075da4ee889cf455.54160770_13r After NSA 350gr BTHP_521.jpg


Note that the pictures are in order of accuracy in my .457 Texan which has a Doug Noble valve, his hammer spring and I use a TalonTunes carbon fiber tank and fill to 3400.
 
Here's the pictures of the .257 Texan re-throating I did at the same time



The .257 throating reamer

1571090843_12475202115da4f19baacbb5.87262176_1r Reamer flutes_153.jpg


1571090855_2282224445da4f1a7e63e54.48166670_2r Reamer markings_847.jpg


In the non-running lathe

1571090868_2200638175da4f1b46646c6.81345346_3r Reamer In Lathe pre feeding_510.jpg


Before and after of the NOE 260-63-WFN-BX1 which actually shoots nicely as a 'plinker'

1571090879_9769005655da4f1bfd8eb88.31027276_4r Before NOE 260-63-WFN-BX1-GC_851.jpg


1571090894_5421352365da4f1ce4607f4.90398386_5r After NOE 260-63-WFN-BX1-GC_617.jpg


before and after of the NOE SC260-80-RF-D3-GC

1571090906_18662028295da4f1da6add28.51538418_6r Before NOE SC260-80-RF-D3-GC_739.jpg


1571090919_6116875945da4f1e7612482.00137696_7r After NOE SC260-80-RF-D3-GC_500.jpg


This is the before and after of the NSA 85gr BTHP which is amazingly accurate in my rifle

1571090941_12737941135da4f1fdbb3b63.76711341_8r Before NSA 85gr_613.jpg






1571090963_2386882285da4f21355db70.18083999_9r After NSA 85gr_336.jpg


The lead before...

1571090991_15290834005da4f22f175852.04205082_lead Pre_134143.jpg


...And the lead after throating

1571091006_18393056195da4f23e5011a9.43644894_Lead after_154708.jpg


Note that the white powder on some of the bullets is part of my anti-fouling system: I use FinishLine Wax chain lube and a tiny bit of MicroLubrol "Hexagonal Boron Nitride" powder (nickname 'White Graphite", which is almost as slick as Teflon) and basically get no fouling with velocities of 1050 FPS for several hundred shots. I put 50 or so bullets in an empty butter tub, squirt in some FinishLine and throw in a pinch of the HBN powder, put the lid on and turn it end for end, tumbling the bullets gently til the bullets are covered. Then dump them out on a silicone baking sheet and let dry.



Also, I now have the new NOE 258-75-FN-BQ6 mold and have cast and shot some and although I did not have it prior to doing this throating job so no before and after pictures it is performing VERY well. It may be my new go to bullet along with the NSA 85gr BTHP.

http://noebulletmolds.com/NV/index.php?cPath=26_603
 
Here's the pictures of the .257 Texan re-throating I did at the same time



The .257 throating reamer

View attachment 60373

View attachment 60379

In the non-running lathe

View attachment 60386

Before and after of the NOE 260-63-WFN-BX1 which actually shoots nicely as a 'plinker'

View attachment 60398

View attachment 60417

before and after of the NOE SC260-80-RF-D3-GC

View attachment 60432

View attachment 60446

This is the before and after of the NSA 85gr BTHP which is amazingly accurate in my rifle

View attachment 60464





View attachment 60483

The lead before...

View attachment 60494

...And the lead after throating

View attachment 60502

Note that the white powder on some of the bullets is part of my anti-fouling system: I use FinishLine Wax chain lube and a tiny bit of MicroLubrol "Hexagonal Boron Nitride" powder (nickname 'White Graphite", which is almost as slick as Teflon) and basically get no fouling with velocities of 1050 FPS for several hundred shots. I put 50 or so bullets in an empty butter tub, squirt in some FinishLine and throw in a pinch of the HBN powder, put the lid on and turn it end for end, tumbling the bullets gently til the bullets are covered. Then dump them out on a silicone baking sheet and let dry.



Also, I now have the new NOE 258-75-FN-BQ6 mold and have cast and shot some and although I did not have it prior to doing this throating job so no before and after pictures it is performing VERY well. It may be my new go to bullet along with the NSA 85gr BTHP.

http://noebulletmolds.com/NV/index.php?cPath=26_603
Do you have any groups testing or targets on how this upgrade did for you
 
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I've been wondering about the details of these reamers...

Is the shape based on saami standards for: bore dia, groove dia, freebore dia and lead angle?

Do you need to buy or make a different pilot for different bore diameters? Just as an example, I have 357 barrels that vary from .347 to .3525 on bore diameter. And what about the freebore? I have 357 barrels from .356 to .3585 on groove diameter, which would all see a reduction in yaw from choosing the perfect freebore and projectile diameter.

Just wondering out loud. I've been doing all of this on my barrels with a cnc lathe and a boring bar to get what I think (occasionally correctly) is best.
 
I've been wondering about the details of these reamers...

Is the shape based on saami standards for: bore dia, groove dia, freebore dia and lead angle?

Do you need to buy or make a different pilot for different bore diameters? Just as an example, I have 357 barrels that vary from .347 to .3525 on bore diameter. And what about the freebore? I have 357 barrels from .356 to .3585 on groove diameter, which would all see a reduction in yaw from choosing the perfect freebore and projectile diameter.

Just wondering out loud. I've been doing all of this on my barrels with a cnc lathe and a boring bar to get what I think (occasionally correctly) is best.
It's pretty standard stuff..All the PTG reamer and theaters were usually pretty spot on with bushing sizes to bore diameter.. Normal powder burner barrels pretty uniform in bore diameter... Too tight bore=too high psi=explosion= thus here in USA they make barrels the right diameter s....Unlike AEA......I used.to make chamber cast at ER Shaw for sample.of bore measurements for quality control... Pretty simple stuff
 
It's pretty standard stuff..All the PTG reamer and theaters were usually pretty spot on with bushing sizes to bore diameter.. Normal powder burner barrels pretty uniform in bore diameter... Too tight bore=too high psi=explosion= thus here in USA they make barrels the right diameter s....Unlike AEA......I used.to make chamber cast at ER Shaw for sample.of bore measurements for quality control... Pretty simple stuff
Sure, standard for PB, but airgun barrels are often different. For example, a recent pair of 357 green mountain barrels were .356 groove and .346 bore. While TJ barrels in 357 were .3585 groove and .3525 bore. Both american, both quality.

Another thought and question... would the ideal forcing cone for an airgun be a different angle than a PB?

I'm not making any assumptions or assertions about these reamers... just raising questions.
 
Sure, standard for PB, but airgun barrels are often different. For example, a recent pair of 357 green mountain barrels were .356 groove and .346 bore. While TJ barrels in 357 were .3585 groove and .3525 bore. Both american, both quality.

Another thought and question... would the ideal forcing cone for an airgun be a different angle than a PB?

I'm not making any assumptions or assertions about these reamers... just raising questions.
As long as you buy the reamers with the removeable piliot bushing reamers. You can buy bushing in any size for that bore you desire. I have the PTG bore indicator rods, finish reamers,and throaters with removeable bushings. I ususally didnt have to change bushings for the piliot that came with reamer...PTG sells any tooling or bushings sizes you could ever want.. Maybe i was lucky mostly benchmark and savage barrels,both pretty decent...
 
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As long as you buy the reamers with the removeable piliot bushing reamers. You can buy bushing in any size for that bore you desire. I have the PTG bore indicator rods, finish reamers,and throaters with removeable bushings. I ususally didnt have to change bushings for the piliot that came with reamer...PTG sells any tooling or bushings sizes you could ever want.. Maybe i was lucky mostly benchmark and savage barrels,both pretty decent...
I say as far as angle in throat powder burner angle should work. Reamers for Subsonic rounds in powder burner have same throats..300blackout for example. shoots 1000 fps and 2700fps same reamer same barrel.. My thoughts????
 
I've been wondering about the details of these reamers...

Is the shape based on saami standards for: bore dia, groove dia, freebore dia and lead angle?

Do you need to buy or make a different pilot for different bore diameters? Just as an example, I have 357 barrels that vary from .347 to .3525 on bore diameter. And what about the freebore? I have 357 barrels from .356 to .3585 on groove diameter, which would all see a reduction in yaw from choosing the perfect freebore and projectile diameter.

Just wondering out loud. I've been doing all of this on my barrels with a cnc lathe and a boring bar to get what I think (occasionally correctly) is best.
I am a gunsmith and I know for a fact that they sell different size bushings as needed
 
I say as far as angle in throat powder burner angle should work. Reamers for Subsonic rounds in powder burner have same throats..300blackout for example. shoots 1000 fps and 2700fps same reamer same barrel.. My thoughts????
I read a book recently that discussed the cone angle a bit. One of the points was how cone angle changes engraving force... with more shallow angles requiring more force. It also mentioned engraving force being a factor in ES of velocity, and cone angle being a factor in in-bore yaw. Curious to know how this translates to our low pressure pea shooters.
 
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I read a book recently that discussed the cone angle a bit. One of the points was how cone angle changes engraving force... with more shallow angles requiring more force. It also mentioned engraving force being a factor in ES of velocity, and cone angle being a factor in in-bore yaw. Curious to know how this translates to our low pressure pea shooters.
Id reasearch the throat angle on a match 22 LR chamber..They are shooting swage lead slugs at 1050 fps. Maybe its different...Pistol calibers like 45acp might be similar too you would think 800 fps.. Your reasearch cant hurt...Accuracy is a pursuit of trying things till you get one hole groups. How ever you do it.. I have a feeling you will find the accuracy you want :)
 
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Nealgl1986, Ideally yes. Ideally just before and slight snug push with the finger to engage the slug into the rifling. But remember if you have the barrel reamed for longer heavier slug when you switch to alot shorter lighter bullet then it'll push to the end of the barrel and the slug lighter slug won't engage the rifling....I try for a happy medium for the different weight slugs. Once I've tested or found the slug the barrel likes I try to have it reamed to the depth for that lenght slug.