Fast burning pistol powder in a rifle length barrel

[SJan]

The new pistol caliber carbine (PCC) division in USPSA is gaining popularity daily. Most of these guys have spent time shooting in Production division where they load 9mm with fast powders to produce a soft recoil impulse in their pistols. It is very convenient to shoot the same load in their new PCCs.

In a facebook discussion, folks are reporting wild chronograph results with their pistol loads in 16" barrels. Some see very small velocity increases, others dramatic increases, some report nearly the same velocity and few actually report a loss of velocity.

I did some chronographing today. The same load (147g coated over 3.3g WST) was fired in several different guns.

4.25" M&P pistol barrel avg. 879fps (129 PF)
5” M&P pro pistol barrel avg. 904fps (132 PF)
8.5” AR9 SBR avg. 993fps (145 PF)
16” scorpion rifle barrel avg. 959fps (140 PF)

My assumptions were correct. With a fast burning powder like WST all of the powder burning energy is used before the bullet reaches the muzzle of a 16” barrel. I’m guessing the most efficient length barrel (for this load) is somewhere are 8-10” Sure you will gain a little velocity in a 16” vs 5” , but the bullet is all ready slowing down as it exits the muzzle.

 

[Hoon]

115gr seem to benefit the most from a long barrel. The same loads i was using for USPSA @1120 were going over 1250fps from a 16" with titegroup and 231.

Winchester white box 115gr was over 1300fps (around 1350 IIRC) from a 16". 147gr HSTs on the other had do 950fps from my G34 but barely hit 1000fps from my 16".

 

[DW357]

I noticed this as I got my first 9mm carbine recently (gen 2 sub 2000). Chronoed some 150 gr blue bullet loads over 3.2 gr of N320 and had the same results you did. About a 40-50 fps increase as compared to my 5" DW PM9.