Rebarrel AR Pistol from .300 BLK to .300 HAMR?

G

Gary L. Griffiths

New member
I have a 7.5" barreled AR Pistol in .300 BLK as my "car gun" primarily for defensive use. I have no need of a subsonic load, so I keep it loaded with factory 110-gr Hdy V-Max, with a couple of spare magazines, and a couple more spare mags with factory 125-gr HPs. I have reloaded a number of rounds with 110-gr Sierra .30 carbine softnoses, and 85-gr Lehigh Xtreme Cavitator bullets. Stiff loads of H-110 will push the latter out of the short barrel at ~2200 FPS.

Both the RN and Cavitator bullets make the load WAY short in the magazine, although I have never experienced any feeding problems with the limited number of rounds I've loaded up. It seems to me that by rebarrelling to .300 HAMR, I would gain a lot of powder space in the cartridge and use up the magazine space with 85, 110 and 125-gr bullets, which could be boosted to quite respectable velocities, even out of a 7.5" barrel.

Would appreciate y'all's thoughts on whether the increase in velocity/power would be worth the effort in rebarrelling the little cannon.
 
CAUTION: The following post (or a page linked to) includes or discusses loading data not covered by currently published sources of tested data for this cartridge (QuickLOAD or Gordon's Reloading Tool data is not professionally tested). USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.

Short answer is no, I would not do it, I do not think not think its worth it.

Not recommending you use any of this load data, this is just want I ran to get some numbers for comparison.

Ran some numbers in GRT with a 7.5in barrel. I used the 110g v-max as well as both Accurate 1680 and H110. ran the pressures up as far as I could go without going over max pressure.

300 ham'r 2033fps 24.8g of accurate 1680
300blk 2003fps 24.3g of Accurate 1680

300 ham'r 2109fps, 22.6g of H110
300blk 2083fps, 22.2g of h110

Near as I can tell, while it does increase case capacity, it does not increase the amount of powder that can actually be used by much. and the velocity gains are modest at best.

Personally I feel that 300blk hits pretty hard as is, not sure why you feel you need more velocity, supersonics are about on par with 7.62x39. But if you REALLY need more velocity id suggest you just get a longer barrel. it would be more effective than changing cartridges. Going from a 7.5 to an 8.5in barrel would get you well more of a velocity increase than switching from 300blk to 300 ham'r.

I simulated changed barrel lengths with 300blk, h110, 110g v-max
7.5in 2083fps
8.5in 2163fps
10.5in 2291fps
14.5in 2472fps
 
Last edited:
Appreciate the info. Was actually more concerned with the shortness of the cartridge with the Lehigh 85-gr bullet than the velocity, as it's already safely duplicating .30 Carbine velocities. Granted, .300 BLK standard twist may not be ideal for this bullet, but hey, not trying to achieve tack-driving accuracy at 300 yds from a pistol! ;)
 
If you were trying to boost performance in a longer barreled hunting gun (16”+) i would consider it.

For a short barreled (7.5”) “ self defense truck gun” where your target is most likely bi-pedal, i don't see the need for more horsepower. I use a 9” barreled 300blk as my go to SD/HD/SHTF rifle. Like you, its loaded with 110gn V-max. If i cant get the job at hand done with that level of power, i need a BIG jump in power. A cpl hundred FPS is just not relevant to the situation.
 
Appreciate the responses. Sounds like it would be more trouble than it's worth, especially since I'd have to form brass and ditch quite a bit of relatively expensive ammo. :eek:
 
You must log in or register to reply here.
Back
Top