Let's talk about spin (barrel)...

[rebby]

I've been debating with myself about how to introduce this topic for a week or so. In the end, I think I'm going to be very brief and simply ask the question to start with and we can go from there. The basis of my question is to help establish the build details for the next run of Lilja barrels that will be 12.5" and 16" in length. The current debate is between maintaining the 1:8 spin or adjusting to 1:7.

What is the preferred spin rate FOR YOU and WHY? What specific performance parameters are most important to you and how does spin rate play in to that for the loads/situations that you experience?

As a basis of comparison, our last run of Lilja barrels (and every Lilja Grendel barrel that I'm aware of) is 1:8.

Thank you!!!

[kmon]

For the Grendel I like 1:8 and my favorite Grendel is a 1:8.4 which handles the 129gr LRAB bullets out to 600 yards very well from the 22 inch tube. Might consider 1:7 if I ever do the a 12 inch barrel build.

On a different note, when I rebarrel the 22-243 it will go from 1:8 to 1:7 for the 90gr bullets. I cn get the 90gr Berger VLD bullets shooting well from the 1:8 barrel but that is driving them as fast as I care to in my rifle and between 500 and 600 yards accuracy starts to be decline

I want a bullet to be stable throughout the distances I will be shooting it.

[A5BLASTER]

For what it's worth my AA barrels use 7.5 twist and they just flat out shoot.

So far me I like 7.5 twist over the 8 twist. But wouldn't have a problem with a 7 twist.

The more twist, the higher the rpm of the bullet as it's driving through and cutting vitals as it's killing a animal.

[JASmith]

it’s hard to have too much spin at Grendel speeds.

[Lemonaid]

1:7 twist will give me one less excuse for a bad group. Can't blame it on marginal stabilization for the longer bullets.

[rebby]

1:7 twist will give me one less excuse for a bad group. Can't blame it on marginal stabilization for the longer bullets.

Do you have a specific bullet in mind that isn't adequately stabilized at 1:8?

[Klem]

Tell you the truth I couldn't answer this question without having both spin rates and doing some shooting.

I do tend to stick to lighter bullets in Grendel, because case capacity is limited and heavier bullets are longer. Longer bullets rob precious powder space when seated to mag length. Monolithic non-lead bullets like Barnes also tend to be larger so I avoid them also. The max weight I have shot Grendel is 123gn and shoot 120's for hunting and 107's for bench. I save the heavier bullets for my 6.5*47 which likes 130AR Hybrids. I know guys here talk about shooting heavier bullets and this seems to be a trend however this doesn't make sense to me because they come out slower (unless you load hot) and even though their stated BC is higher their actual BC is lower and this, and the length of time they are in the wind means means they are more influenced by it.

Twist rate is of course a trade-off between spin to stabilise the likely bullets and having too much spin which exaggerates the imperfections in every bullet. Plus, over-stabilised bullets resist pointing down at the target after apogee (2/3 of way to the target). They present a slight angle to the wind and this translates into bigger group sizes which of course is the reason for not wanting too fast a twist.

Back to your question...I guess it would depend on what is the likely type of bullet used in these short barrels. If guys who buy them understand the implications of slower velocities and shoot lighter bullets to compensate (100-110gn) then 1:8 might be fine.

[Lemonaid]

Do you have a specific bullet in mind that isn't adequately stabilized at 1:8?

Short answer is no.
Long answer is no, just a vague possibility that the Sierra 130 Game Changers would do better with a faster twist.
Given the choice I would go with the faster twist just to remove any mental doubt even if unjustified.

[Redomen]

I’m shooting 123 SST and 129 ABLR in my 12.75” pistol with 1:8 twist and it works well. I would guess 1:7 would work well also but have no experience behind a barrel with that twist rate. I tend to use the heavier bullets because 90% of my shooting is at hogs and deer.

[VASCAR2]

I trust Bill Alexander’s testing, short barrels (less than 16 inches) I’d use 1:7.5 twist. Anything longer than 16 inches I would use 1:8 twist. I have a 16 inch and 20 inch 6.5 Grendel AR-15’s which are both 1:9 and they shoot 123 grain better than I can shoot. I have yet to shoot bullets heavier than 125 grains in 6.5 Grendel. I have a 16 & 18 in Faxon group buy barrels in 1:8 twist If I can’t get the heavy bullets to stabilize in 1:9 twist. I think the longer barrels 20+ inches) can get by with 1:9 twist. I say this because the 264 Winchester Magnum used 1:9 twist for decades and they are very accurate.

[grayfox]

1:8 has been fine for me, up to 129 Ablr and 129 sst. If maybe there were a 7.7 or 7.5 maybe slightly better, but 1:8 is a std with no compelling reason to do otherwise Imo. If anyone looks at resale values then 1:8 is again, an understandable standard for more buyers than any different twist.

[ricsmall]

it’s hard to have too much spin at Grendel speeds.

I agree with JAsmith. At Grendel speeds, I don’t think you’ll over twist the pills in a 7 twist, though you may lose some velocity and experience some pressure sooner with the heavy pills. All of this is complete speculation. If possible I think I would go with the 7.5 as bill alexander has already done the legwork and established some parameters to follow on the 16” and shorter barrels