Quote History Originally Posted By supercrew:
. . . I would like to know more about lapping the front of the upper, and bedding the trunion. Any links to how to's on this process would be good. As I mentioned all my kits have came with pre-installed barrels so I've had no experience in this area, but I'd like to eventually try this.
For future reference I assume a 1:9 or even a 1:12 twist be better for a rifle dedicated to shooting 55gr? I have a friend that is getting 1 moa groups with a cheap government profile Wylde.
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There are plenty of YouTube videos still up on this process. Here is one of the better ones I recommend watching on the process:
https://youtu.be/YqTtjhQ_1RYHe states that for him doing this has tightened up his groups by a 1/4-MOA smaller then before doing it. I on the other hand have seen my group sizes cut in half by doing this. All depends on how out of true the front receiver face was to start with and how loose the trunion fit was in the receiver to start with. Using more budget components (that would be me) it seems to make more difference.
As to twist rates - it's not just twist rate - but combination of twist rate and barrel length. With a shorter barrel you need a little more twist for the same weight bullet.
If you want to shoot 55-gr. lead core jacketed bullets then for a 16" barrel carbine (or a 14.5"-to-15" barrel with pinned and welded permanent muzzle device that brings it out to 16") then a 1:9 twist does quite nicely. But you wouldn't want to run a 1:12" twist barrel that short. 1:12 twist is for 20"+ full rifle length barrels with 55gr. lead core jacketed bullets.
The length of the bullet outside of the case from tip to tail is what matters for twist. Longer (heavier) bullets of the same caliber need a higher RPM to stabilize. Shorter (lighter) bullets of the same caliber need a slightly slightly lower RPM.
Twist rate in a barrel makes the RPM equivalent to the velocity. If for example a longer barrel gives you 20% more muzzle velocity then if the twist rates in both barrels were the same the RPM would also be 20% higher as well. So longer barrels that produce higher velocity with the same load sometimes need a slower twist so as to not overspin the bullet. Shorter barrels may need a faster twist so as to not underspin the bullet.
Best accuracy for each bullet will be helped by being spun up to a specific RPM range that works best for it. Overspin above that range or underspin under that range and it hurts the accuracy.
Some people call it "putting the bullet to sleep". The analogy there is rocking a baby in a rocker to get it to sleep and stay sleeping. Rock too slow and it don't work, rock too fast and it also don't work. Different babies require different rocking speeds.
With bullets and spin it's similar but at least it's more consistent and predictable with bullets. Long bullet for caliber = faster. Shorter bullet for caliber = slower.
1:7 twist is the fastest twist rate commonly available, so unless your shooting a really short pistol barrel it's going to put longer bullets to sleep the best. Longer length bullet usually equals a heavier bullet. Although can also be accomplished by using a bullet of the same weight but made from materials that are less dense. Solid copper bullets for example are usually noticeably longer for the same weight then lead core jacketed bullets.