Weirdness - first shot out of mag always low

[Dogtown]

So here's something I've never seen before.

Was dialing in a new load for an MR762 I've had for ages, using 178 ELD-X with Varget, and got this repeatable situation where the first shot in every 8-shot string was consistently low. I only brought one mag to the range, so this is the same mag loading only one string at a time. My first thought initially was it was a strong cold bore offset, but after I loaded the second string, it repeated, and then the next.

Maybe it's the mag doing something to the first cartridge? But still, isn't that weird?

 

[jetjock07]

Is the first round slow compared to the rest of the string?

 

[Eagle1899]

Are you using the bolt catch to close the bolt or pulling the charging handle all the back and letting it go?

 

[Dogtown]

Speeds are consistent in the string. Closing the bolt with the bolt batch. I’ve had this rifle for almost 10 years shooting a variety of my own loads, but I’ve never seen behavior like this.

 

[Eagle1899]

I would check over everything. Barrel nut, rail, scope, rings, bolt and carrier. If you don't find anything, I'd change the action/buffer spring.

 

[OkieMike]

Does it matter how many rounds are in the magazine? I mean if you only put 3 or 5 rounds in instead of 8 (you did say 8, correct?) does it still throw one low?

Mike

 

[Dogtown]

It was 8 rounds every string, so not only will I try multiple mags next time, but I’ll also try varying amounts. It may be the mag, but the semi-educated scientist in me wants to understand the mechanism that would cause a consistent flyer like this?

 

[Eagle1899]

I have had a well used action/buffer spring cause similar issues closing from mag catch as apposed to the action cycling automatically. The travel and force from bolt catch is different than the regular cycle rate. Last round lock back can cause group issues as well.

 

[OkieMike]

It was 8 rounds every string, so not only will I try multiple mags next time, but I’ll also try varying amounts. It may be the mag, but the semi-educated scientist in me wants to understand the mechanism that would cause a consistent flyer like this?

I get it. I'm curious as hell to see what the issue might be myself.

Try different mags... Vary the round count in the mags... And see if loading the first round with the charging handle (instead of releasing the bolt catch) makes a difference.

Mike

 

[hlee]

It was 8 rounds every string, so not only will I try multiple mags next time, but I’ll also try varying amounts. It may be the mag, but the semi-educated scientist in me wants to understand the mechanism that would cause a consistent flyer like this?

Load 8. Fire 1. Eject the loaded round. Top up magazine to 8. Fire again. Repeat.

Load 1. Fire. Repeat…

 

[cas6969]

Stop mid magazine, eject the round and measure the COAL compared to the original load. Wondering if some pulling or setback is happening when fired, that isn't happening dropping the bolt.

 

[db2000]

Thanks Biden. I’m sure it’s his fault.

 

[47chevycoe]

I have seen a suppressor cause a group with a first round low. But it looks like you’re unsuppressed?