Which high end FT gun?

[thomasair]

Here is some data from this past weekends GP match in Phoenix.

Temps started off in the high 50s and ended up in the 90s.

I chronied and checked temp before and after each day. Velocity gain was 4 fps over the 30 degree plus temp gain from morning to afternoon on my rifle, and Riz Marquez reported similar data on his Thomas.

My rifle and scope were kept shaded, so they stayed at ambient temp throughout the day. I also checked temp on others scopes that were not kept under an umbrella, and the temps were 10-15 degrees higher.

I helped tear down the course, so I got to look at probably half of the long targets after the match was over. Lots of high shots. Worth keeping in mind if you plan to shoot somewhere with large temp swings over the course of a match.

Mike

 

[Franklink]

Mike,

You got my wheels turning in an earlier post when you mentioned that you designed resistance to temperature induced shifting poi into your gun. Now that you've mentioned it again, I'd like to pick your brain.

Is your guns propensity to avoid what we see with changing temps due to the alloy you use? Or pressure tube wall thickness? 

Without divulging possibly proprietary information, how have you achieved this?

I've been under the impression that guns shoot a little faster when they're sun-warmed because the pressure in the vessel is higher. Is there more going on than that?

Thanks

 

[tricker]

Regarding the infinitely informative post on previous page ,I believe the proper response should be: "Please, sir ,May I have another ?"

Yellow classifieds have a SteyrL110 & a Thomas today.

 

[Kdog]

I like the higher shot count of the RAW and that I could order whatever barrel I wanted on it....the entry price of a Thomas was out of my league. I believe the wait time on a RAW is 12 weeks....that's exactly what it was on mine when I received it in December.Perhaps demand is higher now?

 

[redcrow]

Ken Hicks tells me RAW builds are running 13 - 15 weeks currently. Martin's been a bit slow answering emails, so my guess would be he's being kept busy

 

[thomasair]

Franklink...

Temperature induced POI shift and temperature induced velocity change are 2 different issues that we should be aware of....although temp induced velocity change will produce a different POI. Some rifles suffer from both, and therefore can have some crazy stuff happening. 

Temp induced POI shift is typically a design problem that occurs because of inconsistent expansion or contraction of components that are in between the barrel and the scope. POI shift can also be pressure induced...meaning that changes in reservoir pressure affect the alignment of barrel to scope. If you don't want the barrel to scope alignment to change over temp or pressure...you just need to look at how the 2 parts are interconnected and make some common sense decisions. Is it a good idea to create a C shaped part and bridge both sides of it with a scope ring? Is it a good idea to hang on to your barrel with a loose slip fit of 1- 1.5" and a couple set screws or would you rather use a full diameter precise fit 3.5" long? Do you wan to affix your barrel/scope mount using long bolts that go around a pressure vessel that is constantly changing? Think about that.

Velocity fluctuation over temp can be the product of a great many things. I get told often that my rifles cannot be temperature insensitive because air density changes with temperature and we cannot control that. That statement is partially true, but the amount of fluctuation that occurs in most rifles is way beyond what is caused by density changes alone. If you remove the other variables...the air density change alone isn't much. An unregulated rifle will usually shoot slower when the pressure inside the tube is increased because strike pressure is the same and greater force on the valve does not allow it to open the same amount. A well regulated rifle will not do this. Much of the velocity fluctuation due to temp change has to do with frictional differences in the strike mechanism. This can be due to part fitment, use of materials that change density greatly over temp, and wrong proportions of valve parts and strike. If you can build your strike mechanism to hit nearly the same over a broad range of temp...and coordinate your valve proportions and tuning to take advantage of that you will remove the bulk of temp induced velocity swing. I realize that doesn't directly answer your question about how to do it, but that's about all I'm willing to divulge. 

Kdog...just for the sake of clarity, the RAW does not get a greater shot count despite using a much larger bottle type reservoir. Valve changes made a while back have greatly increased efficiency and temp stability. What people know about my gun today will probably not be true in 6 months. I'm constantly moving forward. I'm not knocking the RAW in any way...just pointing out that it does not get more shots per fill.

Mike

 

[ocedummy]

I shot my CF bottle RAW, which gets over 100 shots per fill at 19 FPE, at the AZ nationals and was doing really good for about 4 lanes and then the misses started, After a few crap lanes I noticed that the pellets were going high even though I had been keeping my gun in the shade most of the time. After too many bad lanes, I panicked, and finally fired at the face plate to determine where the pellets were going, 2 dots high and 1 to the left, so after that I compensated for the shift, but too late for a decent score. I have not shot in bright sun before and it is a lot more stuff you have to plan for. Once the gun cooled off, back almost to the original POI. I was thinking of getting a Thomas last year, but with a 15 inch barrel so it can be used as pistol or rifle, and no moderator, they are LOUD and one fill will not make a 50-60 shot match. Still thinking a Thomas Rifle may be good, but, I can buy 2 Steyr's from Europe for the price of one Thomas. A Steyr HP Hunter is $1850 plus $30 shipping, mmm. Too many choices and I do love my Crown .25 and waiting for a .177 barrel kit for it.

 

[thomasair]

The Thomas 15" carbine that can be used as a pistol gets 75 shots at 20 fpe, and about 175 at 12 fpe. As I said above, the new valve has increased the shot count and softened the report as well. They are pretty quiet with the shroud.

Mike 

 

[Franklink]

Thank you Mike. I like the science of airguns and your explanation clarified some things on the topic of temp-related poi shifts. I very much appreciate it.

 

[Kdog]

Mike,
I have a RAW TM 1000 shooting 19 ft lbs and I am getting 125 shots before it falls off the regulator. I also have a Steyr LG110 set up at 19 ft lbs which gets about 60 shots per fill. Im pretty confident that my RAW is getting more shots per fill than my Steyr. More than double to be exact.
I have no idea what your rifles get per fill at 19ft lbs but I was not referring to your rifles in that statement at all.I would be surprised if your rifles got more shots per fill than my RAW TM 1000 with it's 480cc bottle though.

 

[thomasair]

I'm full of surprises! The regular size Thomas does, indeed, get more shots per fill than your RAW with the big bottle. Over 150 at 20fpe on 3200 psi fill.

Mike

 

[Kdog]

Wow that is impressive for sure.

 

[Biagio26]

I own two steyrs lg 110, an AA ev2 mk IV. Now the Steyrs are awesome rifles for what they are. If I could pick one gun, that will be an awesome ft rig, it has to be the new Anschutz 9015 ft rifle. Now the Thomas rifle are aweaome. Oh and don't forget the FWB 800, these are awesome rifles as well.

I hope you make a good choice. 

Biagio

 

[Uglyjohn]

Ok, I ordered a dedicated high end FT gun. Despite Mikes compelling reasoning, I'm getting a RAW TM1000 LH thumb hole RH action. Main reason is that I own a couple of Martins guns and I'm totally pleased with them. The dealer highly recommended getting the poly bbl set up for the 13.43 JSBs. I see that most of the comp. shooter use the 10.34s or lighter. What are the thoughts out there re this? Uj

 

[thomasair]

The Monsters are better in the wind than the 10.34s. If you are shooting hunter the 10.34s have a flatter trajectory, due to the higher velocity, that can be slightly helpful since you will not be able to range the long targets very accurately with 16x. It's very little, though....and it's a trade off for wind resistance.

If I shot Hunter, I would use the monsters and work on ranging.

Mike