Re: 6.5 barrel twist for 139 to142gr
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bone318</div><div class="ubbcode-body">@ Frank - guys are getting better velocities. not huge, but noticeable. FYI, thanks for all of the group buys you all have done for the NCPPRC. I am running Bartleins on all my rigs and love them.
jerry </div></div>
Hey Jerry! Thanks for using the sticks and that you guys are liking them!!!
The number of grooves with the bore surface area being different etc....should have no bearing velocities. Very interesting.
Also a variation of up to a 100fps. is normal from barrel to barrel etc... I remember years ago we made two barrels back to back s/n's etc... for Warner Tool. One barrel went on Al's gun and another for a close customer of his. Both barrels where <span style="font-weight: bold">4 groove .30cal.</span> As identical you could make two barrels. One barrel was a <span style="font-weight: bold">flat 100fps faster</span> than the other.
It would be interesting to know what 4 groove barrel they are being compared to. I don't care about the maker but what I would like to know are the bore and groove sizes/dimensions, groove width etc....what I'm saying here is what does the actual bore size measure and groove size. A tighter or looser bore and or groove size can have a huge bearing on what a barrel produces for velocity.
Is the same chamber reamer being used in the barrels that are being compared? This is another variable.
Bugholes, I don't think there would be a big difference in between a 1-8 vs. a 1-8.5 twist. I would say it would depend on what it's chambered in and velocities you are getting that this will effect over stabilization and bullets coming apart etc.... another thing that effects bullets coming apart are the bore sizes. A tighter bore where the rifling is cutting into the bullet jacket more will have an impact as well. If you are shooting some bullets with a thinner jacket and the rifling is cutting deeper into it this will cause stress points on the jacket and if it's cutting thru the jacket to the core these are things that are going to cause the bullets to fail as well. I also feel that the 5R with the gentler angles and the odd number of grooves will help distort the bullet jacket less and this will help with bullet failure.
You start combining a tighter bore, faster twists, higher velocities the style of grooves, a thinner jacket bullet is all leaning towards producing bullet failures in my opinion. Again there are just a ton of variables.
Spinning the bullet faster if you are shooting a poorer grade/quality type bullet or if your ammo has a lot of run out I would agree with as a start as this can and will have an impact on accuracy.
Back in 2008 we made a 4 groove and a 5R barrel both 1-8.5 twist for Berger bullets and they also got some barrels from another barrel maker and they did testing on velocities, bullet failure and they beat the crap out of the bullets and loads on the ammo etc....and if memory serves me right velocities where not a big concern but bullet failure was.
Later, Frank
Bartlein Barrels