Huldra upper 5.45 X 39

[scaatylobo]

I had to T&E my Huldra upper in the rusky caliber of 5.45 X 39 as the gas system [ piston ] had frozen [ was told that is impossible ] and they sent me a new one .

So can anyone explain why the 16" barrel was grouping fine at 25 yards [ 3" w/o trying = rapid fire for T&E purpose ],BUT when I went to 100 yards the group was still 3" but now was 8" high ?.

This is 1980's mil-spec ball ammo and I was wondering if that is a ballistic Russian thing.

I have NO such problems with the 5.56 X 45 round.

The sight is a 1.5 X 4 power scope that was checked and as tight as could be.

the groups were consistant,did this about 4 times.

For a total of about 80 rounds.

 

[adelbridge]

The scope is mounted very high on an ar-15 rifle. Sight in at 50 or 100 yards. Measure the distance between bore and scope centerline on your hunting rifle and compare.

 

[scaatylobo]

Not on this one

The scope is mounted on the flat top and as low as can be done.

Sighted in at 25 yd's and I was under the impression that should be almost MOA at 100 yd's ?.

Groups are the same size,but WAY to high.

 

[RCArms.com]

If the group size is consistent, I'd be looking at the optic or mounts first.

Don

 

[adelbridge]

The scope is mounted on the flat top and as low as can be done.

You have to measure from the center of your scope to the center of the bore. The AR was not designed for optics and the M4 upper is an adaptation. The scope is mounted way higher than a bolt gun even with low profile rings. I have sighted in at 25 yards and was shooting over the target at 100. The way to do it is to sight in 4 inches low at 25 yards and move out to 100. Put 4 targets up and aim for center of the 4 targets and make adjustments from there.

 

[scaatylobo]

Thank you,but ?

I really appreciate the input.

But I have shot AR's & M-4's for a few decades and I did the 25 yd and then the 100 yardage was spot on.

Can you explain why it did not work this time.

thanks

 

[Andrew Wyatt]

crank about 5 inches of negative elevation and you're golden.

 

[adelbridge]

But I have shot AR's & M-4's for a few decades and I did the 25 yd and then the 100 yardage was spot on.

Can you explain why it did not work this time.

the simple answer is 5.45X39 = different ballistics

it could be barrel harmonics, could be ammo. I have seen a 2" POI shift with different ammo brands. I have seen a 3" POI shift with different muzzle devices. Your hand guards could be gripping too tight. If the ammo is grouping your optics are most likely working fine. Sight in for what ever distance you plan on shooting and dont over think it. I hunt with AR-10s sighted in for 100 and know I have to aim 4" low if something steps out at 10 yards, just one of the AR quirks you have to deal with.

 

[scaatylobo]

@adelbridge

Thanks,best solution so far.

I can use the scope to shoot Kentucky windage easily as the crosshairs are set well for that.

 

[Rob G]

I found some ballistics data over on AR15.com about the 5.45 round. Now this was using 7n6 with a 25 meter (27.34 yards) zero and a pretty low optic. It doesn't say what the gun was but probably a standard '74 so figure 16 inch barrel with a roughly 1:8 twist. At 100 yards the shooter was hitting 4.5" high on average.

I have no idea how all that data compares to your setup or what actual changes would occur but my experience with the cartridge in my '74s is that it does tend to rise a fair bit at first, even with a close zero point.

 

[scaatylobo]

@Rob G

That was very interesting and about what I got from the M-4/Huldra barrel at 16".

I will be shooting it at 100 & 200 yards to see if it comes back on and at what distance.

Then its just a matter of using the scope [ might get a different one ] that has enough graduations on horizontal to not have to adjust scope at any range.

Thank you.