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No. 4 7.62 Mexican Match Range Results

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britrifles View Drop Down
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    Posted: August 03 2019 at 2:50pm
A few weeks back I loaded up some 7.62 NATO “Mexican Match” to test out my theory on why the No. 4 7.62 conversions did not shoot well.  My theory was wrong.  But I did discover something that I’ve not heard before as a possible cause or contributor. 

Here are the Loads:

1. Canadian Dominion Arsenal (DA) 1959 Ball (147 Hard Point Boat Tail) military Service issue

2.  DA ‘59 above, with 150 gr SMK subbed for the 147 gr ball projectile.  

3.  DA ‘59 case, CCI #200 Primer, 42.0 gr Varget, pulled 147 gr DA ‘59 ball projectile from 2 above.  

4.  DA ‘62 case, WLR primer, 40.0 gr Varget, 168 gr SMK as a control (proven match load).  

I expected load 2 would be best of loads 1 thru 3.    It was not.  

2 x 10 shot groups of each load off the bench at 200 yards, PH 5C aperture sight.  This is a UF56 Mk 2 action with CA 7.62 barrel, mid-band barrel bedded.  




Here are the targets.  Note there was some sight adjustments between groups as noted.

Load #1 DA 59 Service Ball, Group 1 - 2.6 MOA extreme spread, not bad for service ammo.



Load # 1 DA 59 Service Ball, Group 2 - 6.0 MOA extreme spread, terrible.  No idea why second group was so bad.

Moved rear sight 1 MOA left before shooting this group.



Load # 2 150 gr SMK subbed in for Service bullet, Group 1 - 2.8 MOA, Fair result, expected better




Load #2 150 gr SMK subbed in for Service Bullet, Group 2 - 5.1 MOA, terrible, expected way better.




Load #3 42.0 gr Varget, 147 gr Pulled Service Bullet, Group 1 - 2.0 MOA much better than expected

Note the shift in MPI, about +4 MOA from previous loads which all has the original factory powder charge. 



Load #3 42.0 gr Varget, 147 gr Pulled Service Bullet, Group 2 - 2.1 MOA much better than expected.

Adjusted rear sight 3 MOA down and 1 MOA left before shooting this group.



Load #4 40.0 gr Varget, 168 gr SMK Match Load Control Group.  

Note the 2 shots that were just outside the X ring (10.9) 1.7 MOA Extreme Spread.  The group was 1.5 MOA for the first 9 shots.



Conclusions:

Poor accuracy of 7.62 Service Ball Ammo was not related to bullet quality.  The two 10 shot groups with pulled bullets loaded with 42 gr Varget grouped at approx 2 MOA extreme spread.  150 gr Match bullets loaded in place of the pulled bullet did only slightly better.  

When loading up these cartridges, I weighed the powder charges of 20 rounds and was surprised it ranged from 40 to 43 grains.  The powder appeared similar in stick size to IMR 4895.  I returned the individual charges back into the case they were dumped from, so load #2 with the 150 gr SMK evaluated the as charged service ammo with a modern match bullet.  

Variations in powder charge weights most likely was the cause of poor accuracy.  I suspect the service ammunition may be loaded to a higher velocity than Load #3 (42 gr Varget), and the higher velocities/pressures may be flexing the action more than the .303 and giving erratic groups.  

I intend on doing two more tests:

1. Pull service bullets, dump powder into powder measure, recharge cases with 40.0 gr of service powder, reseat pulled service bullet.

2. 42.0 gr Varget with 150 gr SMK.








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britrifles View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: September 06 2019 at 3:47pm
Spent the day at the range.  I could see the drop in my performance from only going once to the range in the last 3 months.  I could not hold steady in prone, could see the front sight moving all over the target.  

I tried several loads today in my 56UF No. 4 Mk 2 with CA 7.62 barrel:

DAC ‘59 Service Issue 7.62 NATO Ball - pulled bullets, dumped powder into measure, re-metered the charges at 39.0 gr thru my Redding measure.  Reseated the service 147 gr hard point BT bullets.  This ammo had a range of powder weights as loaded from 39.8 to 42.2 gr from 40 rounds.  

The results were much better than shooting the ammo “as loaded” and also better than the 150 gr SMKs subbed for the service bullet keeping the original powder charge.  




I was surprised how well these service bullets shot.  10 rounds, 200 yards off bench, 3.7 inch center to center (1.8 MOA).  Shots 9 and 10 scarred the edge of the X ring, a hair off a 100-9x score.  

Of the 40 rounds I shot with these pulled bullets and re-metered charges, there was 4 fliers in what would otherwise be sub 1.5 MOA groups.  This service ball ammo has very inconsistent powder charge weight causing vertical dispersion (as seen in the targets in the OP with both the service bullet and with the 150 SMK) and approx 1/10 fliers likely due to bullet quality.  Even still, for service ammo, groups were respectable.  


Conclusion

The No. 4 in 7.62 had a reputation for not being as accurate as the .303 on the target range.   My conclusion is  this was likely due to sub-standard quality/consistency of the loaded service ball ammo. 

I don’t know if the NATO accuracy standard for the 7.62 ball cartridge was less than the .303 standard, but I can say that for several .303 service loads I’ve tried, the .303 performed better than the 7.62.  Perhaps this was what the British NRA and Canada DCRA struggled with in the 1960s as they converted their .303’s to 7.62 for Service Rifle match shooting.  

Short Range Load

For something completely different, I tried this load:

Case - DAC 1962 Neck Sized
Primer - WLR
Powder - H4895, 42.0 gr
Bullet - 125 gr Speer TNT varmint
COL - 2.70 in.

200 yards, prone, 10 shots:



Shows how unsteady I was in prone today, walked it all around the outside of the X ring.  Group was 2.6 MOA. Nice light recoil and makes a good short range load or varmint load. 




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