[chasseur]

Gaining experience with my HK MR762A1 running with an OSS BPR1/SRM6. Before attachment of the suppressor, a variety of 168 g match .308 and 7.62 fed and cycled flawlessly with fine groups and no case or primer issues. With the suppressor attached, ATOMIC 175 g subsonic match fed, chambered, fired and grouped fine (no cycling with this subsonic). With IMI 168 g match ammo suppressed, I am seeing some case-head swipe (image uploaded).

Haven't tried the Federal match ammo suppressed yet to see if it experiences the same issue.

Anyone have similar experience with case-head swipe when running suppressed?

Any thoughts appreciated.

 

[THRLSEKR]

I own a MR762SD kit with the OSS BPR1425 and SRM6. While I waited for the OSS to get out of jail, I ran my SureFire 7.62 RC2 SOCOM on it with 168 FED MATCH, your same ATOMIC 175 Subsonic and ATOMIC 175 Match with no issues, although I didn't give the brass a real hard look.

Last week I just got around to running the new OSS can. Through it I only put the ATOMIC 175gr SUB through it and agree, grouped fine w/o cycling. I then tried to run Winchester 147gr white box, that I use for a G3K sbr 12.5"bbl, and was surprised to learn it would NOT cycle suppressed. I consulted with a buddy who has the same set-up and he told me that the Win. 147 is notoriously underpowered. Okay, I must test more. I'm sorry I didn't bring more variety of 168 Federal Match and ATOMIC 175 match, but I was shooting in my friend's yard at 75 yards. I know this doesn't necessarily answer your question, just a little OSS info here.

To clarify, by "case-head swipe" are you talking about the dimples at 12 o'clock on your photos or the fact that the way you oriented the cases, all the primers look 'smushed' around 9 o'clock???

Is the IMI factory or are you loading them? If you're loading them, could the primers have seated slightly crooked? Could there be a small crumb of grit in your primer-seating head or are you questioning back-pressure?

 

[THRLSEKR]

@mew check this out

 

[mew]

overgassing as I have stated before but you would expect that with no adjustable GB
there is a good amount of info here;
Case head swipe from a .308 Jp LRP07 .... Help please. | Sniper's Hide Forum

good explanation here;
https://www.shootingillustrated.com/articles/2011/4/12/case-head-swipe/

 

[THRLSEKR]

Great article Mark! I hope this helps the O.P.

 

[chasseur]

I own a MR762SD kit with the OSS BPR1425 and SRM6. While I waited for the OSS to get out of jail, I ran my SureFire 7.62 RC2 SOCOM on it with 168 FED MATCH, your same ATOMIC 175 Subsonic and ATOMIC 175 Match with no issues, although I didn't give the brass a real hard look.

Last week I just got around to running the new OSS can. Through it I only put the ATOMIC 175gr SUB through it and agree, grouped fine w/o cycling. I then tried to run Winchester 147gr white box, that I use for a G3K sbr 12.5"bbl, and was surprised to learn it would NOT cycle suppressed. I consulted with a buddy who has the same set-up and he told me that the Win. 147 is notoriously underpowered. Okay, I must test more. I'm sorry I didn't bring more variety of 168 Federal Match and ATOMIC 175 match, but I was shooting in my friend's yard at 75 yards. I know this doesn't necessarily answer your question, just a little OSS info here.

To clarify, by "case-head swipe" are you talking about the dimples at 12 o'clock on your photos or the fact that the way you oriented the cases, all the primers look 'smushed' around 9 o'clock???

Is the IMI factory or are you loading them? If you're loading them, could the primers have seated slightly crooked? Could there be a small crumb of grit in your primer-seating head or are you questioning back-pressure?

Yes, the "case-head swipe" is seen at the 12 o'clock position. I did orient the brass to show it the same way on all. I've experienced no blown or popped primers; I think the lighting in the photo may be the cause of the appearance of the primers. I am using only factory loads.

I have read both articles by Richard Mann from Shooting Illustrated and the thread in Sniper's Hide Forum provided by MEW: and [URL="https://www.shootingillustrated.com/articles/2018/6/12/3-warning-signs-on-your-range-brass/"]https://www.shootingillustrated.com/articles/2018/6/12/3-warning-signs-on-your-range-brass/

In his first article Mann reported that he experience CHS when dwell time was increased by heavier bullet weight. I will try shooting some factory IMI NATO 150 g FMJ with the OSS in place. Perhaps lowering the bullet weight from the 168 g match will help. I'll report back with results.

Thanks to all for the comments.

 

[mew]

very interested in your results since I haven't shot mine with the OSS yet, keep the info updated chasseur!!!
THRLSKR has had some interesting results also with the WWB 147gr. not cycling which surprised me, the subs
not so much as it's to be expected.

 

[THRLSEKR]

That's what the forum is all about! I didn't have "the" answer, but knew MEW would know where to look....

 

[FNFNC]

I had that same OSS can on my MR762. Absolutely hated it!! It was so loud that I had my friends saying “that’s suppressed”? The poi was constantly changing. Sold it. I was running FGMM 168gr. No problems cycling.

 

[mew]

that's disappointing, will be trying mine out soon. but I have read the opposite reports also where the user says
it's crazy quiet and super soft shooting. lowered expectations I guess. at least my Omega works great and will replace the OSS if need be.

 

[chasseur]

that's disappointing, will be trying mine out soon. lowered expectations but I have read the opposite reports also where the user says
it's crazy quiet and super soft shooting. lowered expectations I guess. at least my Omega works great and will replace the OSS if need be.

Seems I owe all an apology. I started this thread without adequate examination of my spent brass. I have gone back to look more carefully and would now like to redirect my questions. I don't think the issue has anything to do with the silencer. For the record, my OSS BPR1/SRM6 has been both quiet and accurate. Your mileage may vary.

The first image is my crude drawing of what I think I'm seeing on the case heads with the partial circles positioned at 12 o'clock. Examples follow in the next images showing 147g,
.308 brass without suppression, 150g NATO 7.62 brass with suppression, 168g Match 7.62 brass with suppression, and Atomic 175g .308 subsonic brass with suppression: all are factory loads. Other supersonic factory cartridges show similar results.

Near the outer edge of the cases, at about 11- and 1 o'clock, there are two incomplete circular imprints. I'm guessing these are caused by the ejectors? There is often a central dimple within one or both partial circles and a line extending from the dimple clockwise to the right. Could the dimple and line be caused by the firing pin? None of these markings are present on the subsonic brass or on unfired rounds.

Throughout, I have seen no issues with feeding, chambering, firing, extracting, or ejecting and no primer issues.

So, it seems that the OSS suppressor is not to blame here. Is this case-head swipe? Are the case head marks on the supersonic rounds the result of excessive chamber pressures or is this normal for the MR762?

Any thoughts or suggestions? I haven't taken this yet to HK hoping members here might provide some guidance.