What effect does the amount of lands have on the projectile?

It seems to me that more grooves/lands means that you'll get better stabilization with less obturation. the lead would not have to expand as much to "catch" enough edges to impart the spin. However less obturation also means more air blow-by. Only a hypothesis but makes sense to me.

Regarding rate of twist in general the higher the sectional density of the projectile, the faster twist you need. Good example in the PB world was when the US went from the M16A1 to the M16A2. The barrels went from a 1:12 twist to a 1:7 twist since the ammo changed to a longer projectile with a higher SD.

legionair said:

Interesting. I hadn’t considered how it affects obturation. It would make sense that the projectile now has to expand more with a greater amount of lands, possibly leading to less obturation. Thanks for the input

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It's only an informed opinion. Been shooting muzzleloaders for decades and round ball barrels have slower twist rates with more and deeper grooves than barrels designed for conical black powder projectiles. The round ball can't obturate into the deep more numerous grooves so a greased patch is used more to help the bullet "catch" the rifling twist. The CW rifled muskets OTOH have very shallow grooves and only 3 or 4 of them depending on the rifle (Springfield vs Enfield). Also a much faster twist rate than a traditional round ball barrel. That's enough for a hollow base Minie ball to obsturate properly. Regards.

legionair said:

I think the grooves in the TJ liner will be shallow like the rifled musket barrels. Although, the muskets have a lot slower twists.

What’s interesting is that some really accurate air rifles have very slow twist (1:28, 1:30) similar to the muskets

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I reckon that's because the SD of even the most accurate airgun slugs are substantially less than long heavy PB bullets of the same caliber:

SD = mass (gr) / (7000 x diameter (inches)^2). By the formula (all nominal 22 cal):
14gr pellet SD=0.0437
25gr slug SD=0.0750
55 gr FMJ SD=0.1566
77 gr FMJ SD=0.2192

If the barrel you are thinking of is a pellet specific barrel then yeah, a 1:30 twist should be great. Even a slug barrel in that twist should be good. Regards

Well il drop my input. Less grooves is better as long as you can get proper rifle engagement and dont have any riflingslipping. Benefits of less rifling to barrel friction are marginal tho when speaking about slugshoot intended airguns they might have more to do with BC of the projectile but that would require individual studies for barrel and each projectile combo to tell difference.
What comes to twistrates you brought up 1:22 and 1:17,7 il just say slower is too slow to shoot any slugs well past pellet weights and 1:17.7 caps at about 50-55gr and if bullet is BT it needs to be under 50gr. So not really ideal for slugs.
I dont personally think its possible to over stabilize slug in airgun velocity and we havent seen any proof of it. But you certainly can under stabilize one and since barrel friction is rather unrelevant force you should alwas choose faster. You cant really have optimal barrel for pellets and slugs since you could literally shoot pellets from straight pipe but need really fast rpm for even light slugs.

LW barrels in general shoot well with slugs. In my Revere .177cal slugs shoots ekstremely well with low speeds too. It may not be the number of grooves alone but how deep the grooves are. I just saw a YT video with a guy from SA who shoots an Impact M3 in .177cal. That gun didn`t do any good with heavy pellets at low speeds in particular with JSB 16,2grain where mine does well at low speeds.

I went 3 groove on my barrel design to reduce friction and the odd number of lands aren't compressing at opposite quadrants so less distortion. Only .025" depth of groove and still getting perfect land engagement.

i think quality of the barrel will matter more as well as a projectile that fits the bore right .. all things being precise, a smaller, higher number of grooves i think deforms the projectile less and probably has less friction .. i would imagine its less forgiving on projectile diameter discrepencies though, and also needs to have a quality finish .. an ole rough 6 groove type cheap aigun barrel finish wouldnt suffice ie it would add cost im sure .. ..

thammer said:

I went 3 groove on my barrel design to reduce friction and the odd number of lands aren't compressing at opposite quadrants so less distortion. Only .025" depth of groove and still getting perfect land engagement. View attachment 297704View attachment 297705

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Interesting. The traditional Enfield rifle had 5 grooves. The Metford had 7. Maybe the Ellis Metford who were the invented of both rifling profile thought that an un-even number of grooves avoided too much compression?.
Lilja barrels also made 3-groove rifling at one time.

do i remember right ? Mac1 have a 2 groove barrel or he tried it ?

thammer said:

I went 3 groove on my barrel design to reduce friction and the odd number of lands aren't compressing at opposite quadrants so less distortion.

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Interesting, I never thought of that aspect.

Here's a question would moly on the slugs help speed them up there for a while moly covered projectiles were all the rage more lands and grooves more bearing surface equals slower velocity and a reason I asked about moly

The primary intent of projectile lube is to reduce leading the bore. A secondary benefit is that it does reduce friction which increases velocity. Link follows to a PB article where they did the experiment. Significant increase in MV with bullet lube.


It stands to reason that lube on an airgun slug will likewise increase velocity. Have fun and do the experiment. Let us know how it goes. Be mindful that the lube is HPA safe but you should be OK with a thin Moly grease film. Regards, Badger

IMHO number of grooves makes no difference as long as they engage enough to spin the projectile. This has been tested countless times in PB world and these days it’s odd vs even number or opposite vs offset groove engagement. Personally I like the ideal of offset groove but at the same time opposite groves ensures better engagement so back to square one! Quality of the barrel has far more to do with accuracy than style of the barrel if you ask me.


Twist rate is a different conversation all together.

beerthief said:

do i remember right ? Mac1 have a 2 groove barrel or he tried it ?

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That would have been the Custom BENCHMARK barrels ... another story for another day on that one !!

the depth of the land was much more important than the number when we did research back in the early 80 -90s for powder burners, however less land were better
octagonal barrels pissed over almost everything
Musgrave used 5 lands on the Musgrave RSA target rifle when everyone else were using 6 or more, and got banned from most international competitions as unfair advantage
twist rate in powder burner general rule is slower twist , heavier projie
thats also been the findings of Mat form airarmshunting when visiting FX they use a gradual twist from what i could gather for heavy slugs