Doc GKR / anyone can you please advise on what the better choice is for a short barrel AK (Krinkov) style SBR between the 5.45x39mm or 7.62x39mm? I am contemplating an SBR build and would like to retain the best ballistics from the overall size package as possible.
At this point size, due to the intended nature of the rifle, is paramount but I want to retain as much ballistic potential as possible.
Thanks.
7.62x39mm
thanks
How short a barrel could you go and still have adequate performance with a load like the Corbon DPX load in 7.62x39?
We have never tried it. The easiest way to estimate potential effectiveness is to contact Barnes and ask them what the minimum upset velocity is for the 7.62x39 mm TSX projectile…
We down loaded some of the 7.62x39 DPX loads to 1800 fps to check this out. We still got perfect expansion with penetration of 18" in 4 layer denim clad 10% ballistic gelatin.
Michael-
Thank you this answers a lot of questions for me and seals the deal in regard to the caliber of my selection. As I already have a significant investment in 7.62 x 39mm magazines and other equipment including rifles this makes the most sense from a logistical standpoint but I wanted to be sure that I was not giving up ballistic potential.
One other question if I may, have you done testing such as this with the 5.56mm? How low can you take the velocity threshold and if so what round is suggested for a 7.5" barrel?
As I stated originally size is paramount with this build so I am even considering a ‘micro-AR’.
We did some work with our 223 loads like this.
If I remember correctly, we began seeing failures at 2100 FPS with our 62 gr DPX load. We didn’t try the 53 gr DPX load. I know the 62 gr load still expanded from a 10" barrel. Penetration was still in excess of 16" in the same test material.
If I get time and material, I will try this with the 53 gr load also. I think that would be the go to load if I were running a short barreled rifle.
I would like to see a TSX loading for the 5.45 caliber weapons.
Anyone have an idea how short a barrel you could go to in 7.62x39 and still get 1,800 fps at the muzzle to about 100 yards?
If you are looking for expansion with low velocity Barnes recently released a 110gr .308" bullet designed for low velocity. It will expand down to 1300fps and was designed for use in the 300 Whisper / 300 BLK / 300 FB / 300-221.
I haven’t tested them yet for expansion but Barnes told me the window was 1300fps to 2300fps. Out of my 10.5" 300-221 I’m getting around 2100fps muzzle velocity. I’m looking into building a 7.62x40 wildcat with a 12" barrel and with that 2300fps at the muzzle should be easy to get.
If you had failures at 2100 does that mean you still got good performance at 2200? If so, that means I would still have good expansion velocity from my 11.5" SBR out to about 160 yards with the 62gr TSX. That isn’t bad and I suspect the 53gr will be even better. I look forward to seeing those results.
I would guesstimate a 9" or 10" barrel would be about as short as you could go. Homeloads might bring the velocity up a bit however, we just tested 5 or 6 various types of factory or surplus.
Edited to add the data:
7.62
Short barrels want larger diameters.
Why do you think pistols have .357 to .450 bores?
For any given pressure limit, the force available to accelerate the bullet is proportional to the area.
More bore gives you more force and more acceleration to get up to speed in a short barrel.
Has there been any data collected on the Hornady V-max 7.62 load out of a short barrel in the 8"-12" range?
Ek