5.45x39 vs. 7.62x39

When you factor in the loss of about 6" of barrel, which Krinkov caliber would be the least affected with respect to terminal ballistics, and why?

Well, as a general rule,  high speed, lightweight cartridges shed more velocity in short barrels than do the low speed, large bore types.

According to Lyman:

For rifles with muzzle velocities in the 1000-2000 fps range, the change in velocity for each 1" change in barrel length is 5 fps. For rifles with muzzle velocities in the 2001-2500 fps range, the change in velocity for each 1" change in barrel length is 10 fps. For rifles with muzzle velocities in the 2501-3000 fps range, the change in velocity for each 1" change in barrel length is 20 fps. For rifles with muzzle velocities in the 3001-3500 fps range, the change in velocity for each 1" change in barrel length is 30 fps. For rifles with muzzle velocities in the 3501-4000 fps range, the change in velocity for each 1" change in barrel length is 40 fps.

Therefore, the standard 123gr 7.62x39 FMJ will lose ~60fps and the 5.45x39 will lose ~180fps.  (This is calculated with your 6" figure...actual Krinks have ~8" barrels, so the numbers would be a little different with a real AKS-74U barrel.)

This really won't affect the terminal ballistics of the rounds, it will only decrease their effective range.  Since the Krink is designed for CQB, the overall effect is nil.  Under 150m, I wouldn't think you'd see any difference in terminal performance.  

Personally, I'd stick with the 5.45x39 in a Krink.  More controllable, less muzzle blast and concussion than 7.62x39.

Straight up analysis Drich.  Well done.

Personally I find the 5.45 to be much, MUCH more controllable in a Krink.  Having built several over the last couple of years, and test firing each one, the Yugo 7.62 Krinks are downright concussive, and the light weight of the gun definitely results in a noticeable increase in felt recoil over a full size 7.62.  

Check out the difference in the Yugo Krink vs. the full size guns in this "MCA Goes Shooting" video I made awhile back.

www.youtube.com/watch?v=U-GOShxCynY

I have always heard and been told that the 5.45 does not depend upon reaching a very high velocity to achieve it's lethality unlike the 5.56 round which becomes more lethal traveling at higher velocities. It's in the design of the projectile, which is just as deadly as it is coming out of a full length AK74 as it is out of a smaller AK74SU, just at a slower velocity and degraded accuracy.

Or at least this is my understanding.

I personally think a 7.62 makes the better transition of the two to a shorter barrel.  

But it's a trade off, the 5.45 is more controllable.
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ETA: Heres a video on the penetration between the 5.45 vs 5.56, it's in Japaneses but pretty self explanatory. I have no idea what type of 5.56 round they are using for the test, but the 5.45 appears to be 7N6.

www.youtube.com/watch?v=9hdLoL0i5Sg&mode=related&search=

Quoted: 5.45x39 vs. 7.62x39 When you factor in the loss of about 6" of barrel, which Krinkov caliber would be the least affected with respect to terminal ballistics, and why?

Good question.  A 6" shorter barrel brings you to 10", so a Yugo M92 Krink would definately fall into that category, but the 5.45 Krink is only about 8.25", so I guess we need to ask the question assuming that barrel length.  

I know that the Bulgarian steel core 5.45 is less velocity-dependant than the 5.56 due to the air pocket, and that the 7.62 is less velocity-dependant than both of the smaller calibers due to it's size, but I am also interested in anyone's ballistic knowledge of the subject. Especially after viewing the video on semi-auto rifle bullet penetration through intermediate barriers.

http://www.youtube.com/watch?v=dKhMOfaYwvE&mode=related&search=

Let's assume appropriate barrel lengths for each design.

I have shot my M92 with the factory muzzle break and with a custom made 4 part Bulgarian FH. The 7.62 with the stock krink break does have a bit of concussion to it but with the Bulgarian 4 part its a non issue.

I think the M92 is a great 7.62 Krink with the 4 part FH

Quoted: I have shot my M92 with the factory muzzle break and with a custom made 4 part Bulgarian FH. The 7.62 with the stock krink break does have a bit of concussion to it but with the Bulgarian 4 part its a non issue. I think the M92 is a great 7.62 Krink with the 4 part FH

Good to know.  Was the 4-piece Bulgy FH "custom made" due to the muzzle thread being different?  I've heard the M92 has some unorthodox thread on it.

The custom "Krink" that we built in 7.62x39 with a 11.5" barrel and Bulgarian flash hider can has litte recoil. Once I took the can off, the recoil was VERY noticable.

Here is the pic that posted of my son holding it...




thanks,
Ron

I appreciate the info on the recoil characteristics of the rifles, however, it is rather obvious which has the greatest recoil across the board--namely 7.62.

That's not the issue. What I'm trying to determine is which round is weakened the most by going Krink, and I think the answer is 5.45, yes?

Quoted: What I'm trying to determine is which round is weakened the most by going Krink, and I think the answer is 5.45, yes?

If you're equating loss of velocity with "weakening", then the answer will always be the faster, lighter round.  

With regard to velocity in this case, the 7.62x39 loses ~2.5%, while the 5.45x39 loses ~7.75% with their respective barrel lengths.

Of course, velocity isn't an absolute indicator of terminal performance, so those numbers are fairly meaningless by themselves.  You'd need gel/barrier testing to determine if the rounds actually exhibit less effectiveness within the designed performance envelopes of the firearm.

I personally prefer the 5.45mm round better in a krinkov. But that is just me. I've always like the AKSU-74. Its a ligher weapon and has less recoil and the bullet is deadly since it has a steel core and a gap of air in it and is high velocity.

Quoted: Its a ligher weapon and has less recoil and the bullet is deadly since it has a steel core and a gap of air in it and is high velocity.

I give up.

Quoted: Quoted: Its a ligher weapon and has less recoil and the bullet is deadly since it has a steel core and a gap of air in it and is high velocity. I give up.

I not even sure what information you want to gain from this thread... not sure you know either.

Are you looking to purchase/make an SBR in one of the common AK calibers?

Are you asking which caliber suffer less of a degrade in accuracy when shortened with respect to, velocity, lethality, etc?  

I'm not sure you'll be able to compare two Krinkov variants with respect to both barrels being the same length... Best you can do is compare existing rifles that were built from kits in available calibers.

Alot of people have given some good information to you? What specifically do you want to know?

Good to know. Was the 4-piece Bulgy FH "custom made" due to the muzzle thread being different?

Yep.
M92 has a bastard thread size. I had the threaded portion of a stock M92 krink FH cut off and the threaded portion of the Bulgy 4 part FH cut off - then I had the M92 threaded portion TIG welded to the bulgy 4 part FH.

End result was fantastic and very much worth the effort. My 5.45 Bulgy krink is easy to shoot with either the stock krink FH or a Bulgy krink FH. There is some difference but its tolerable either way. With a 7.62 krink - the 4 part FH is the only way to go IMHO*


* unless you supress it with a can...but thats a whole other 'can' of worms - nobody makes a 7.62x39 suppressor anymore. AAC did for a while but they stopped. If you want a 7.62x39 can nowadays it will either be used or custom built by folks like David Winston of Shark Suppressors or Murray Urbach...both are great cans