What’s Causing these Grooves?

Braces Airgun Masters
Possibly you stalk with a very full
Mag and empty chamber, then you pull the bolt back over the top round in the mag, which is pressed to full and no spring ‘give’ left, so bolt drags over them. The one with two lines you might have done it with twice. You might see it only 3/50 times if the other times you’ve fired the shot, or ejected the unfitted round, leaving the one below with spring give, and it won’t happen. I bet you have a single stack mag as well
 
HonestJohn said:
Possibly you stalk with a very full
Mag and empty chamber, then you pull the bolt back over the top round in the mag, which is pressed to full and no spring ‘give’ left, so bolt drags over them. The one with two lines you might have done it with twice. You might see it only 3/50 times if the other times you’ve fired the shot, or ejected the unfitted round, leaving the one below with spring give, and it won’t happen. I bet you have a single stack mag as well
Click to expand...
👆 Bingo !
 
It was at the range, with a 10 round single stack mag, but only loaded with 5 rounds. It was whilst at a guest day, so newbies using the rifle, it may be down to them not loading it properly…… Obvs not my fault 😁

Your logic does make sense though, I do think it’s the bolt dragging across, so could’ve been newbies not used to it, although I was there supervising and didn’t see anything untoward, apart from the usual cack handed loading of those inexperienced……

Off to the range again this morning, and getting it checked over to rule out anything wrong with rifle/bolt though.
 
Are those small dents at the shoulder and the beginning of the scrapes?
What bullet are you using, is it loaded short and resulting in difficult chambering?

I'm just wondering if the round is not aligning properly with the bore and if rather than a slick chambering some effort is required to chamber the round. Resulting in a scrape and a small indentation to the shoulder. The case with two marks/grooves may have been tried twice perhaps.
 
That is being caused by something ‘mechanical’ interfering with the case as it’s moving forwards. The marks are identical on each case, even the two on the one case are duplicates of each other. There is an initial impact park at the front on the shoulder & then a scrape that tails off towards the base of the case.

You haven’t said what rifle it is but to my mind this looks as if it’s being caused by the round hitting something on the way forward, like the edge of a metal magazine, or it’s the bolt hitting it as the round is in the magazine underneath & the bolt is drawn back over the top of it.

Whatever it is, it shouldn’t be happening as it’s suggests something is quite a long way out of tolerance & may well be broken. If it were my rifle I’d stop using it until I could diagnose the cause & then rectify it.
 
Another 30 rounds fired, nothing untoward, I’ve inspected everything and it looks all good, still getting it checked over though..

It’s a Tikka T3 .223 using MDT magazines
 
Could be caused by a number of things

All could be checked by yourself

Examine the chamber mouth for sharp edges and the magazine at the point the case bears against when being fed

Any sharp edges will cause a mark

Load a set unmarked case s in mag and feed one / extract and examine for marks

If there is then do the same again slowly and look where contact is being made

It could also be the bolt lower surface bearing on the case under the one being fed

You should clean your chamber too and get rid of the damn boresnake

They are utter shite and cause more issues than they are worth

Snap one in the bore and you’ve a ruined barrel
 
That’s a fairly significant dent in the cases…. Load slowly you’re bound to feel the time when it happens. It’s gonna take a little force to do that so you should feel the “that’s not normal”. There’s half a dozen things it could be… just work through the process.
 
fordy1967 said:
Another 30 rounds fired, nothing untoward, I’ve inspected everything and it looks all good, still getting it checked over though..

It’s a Tikka T3 .223 using MDT magazines
Click to expand...
Keep us posted please on what you found. Might just save the next guy from struggling to identify this problem.
 
Hi all, nothing untoward and no further repeats. It must’ve been my guests not pulling the bolt back and forth properly
 
Hey all, ok, at the range today and was having trouble picking up rounds, that’s definitely what’s causing the grooves, it seems the mag is loose and needs to be pushed up a little to allow the round to be picked up. I’m using MDT plastic mags in a KRG Bravo chassis. Before I bin the mags and buy some different ones, is there anything I should try first, or is it a case that the mags aren’t good enough?
 
Hi fordy a quick search came up with this don’t know if you have tried any of them

MDT .223 magazines, both polymer and metal, can experience loose fitment, failure to pick up rounds (nose-diving), and feeding issues, particularly when used in Tikka, Howa, or Remington 700 chassis systems
. These issues often stem from the magazine sitting too low in the magazine well, preventing the bolt from grabbing the cartridge, or due to weak/improper spring tension.
Here is a breakdown of the common causes and solutions based on user reports:

Common Causes
  • Magazine Sitting Too Low: The magazine does not sit high enough, causing the bolt to ride over the top of the cartridge, often referred to as "nose-diving".
  • Loose Fitment: The magazine wobbles in the magazine well, which can be caused by tolerance differences between the magazine and the chassis.
  • Weak or Incorrectly Positioned Springs:The follower spring might be weak, or the spring/follower is binding inside the magazine, preventing proper upward pressure on the rounds.
  • "No-Binder" Plate Issues: Some MDT metal magazines without binder plates may cause the tip of the cartridge to catch on the chassis.

Solutions and Fixes
  1. Adjust the Magazine Latch/Catch: Many chassis systems (like MDT LSS or XRS) have adjustable magazine latches. Tightening the latch allows the magazine to sit higher in the chassis, improving the feeding angle.
  2. Contact MDT for New Latches: If your chassis has a "loose" fit, contacting MDT support has led to them sending updated or different-sized magazine latches to resolve the issue.
  3. Adjust the Feed Lips (Use Caution): If the cartridge is not presenting high enough, you can gently adjust the feed lips on metal magazines. For polymer magazines, some users have used boiling water to soften and slightly bend the feed lips together.
  4. "Break-In" the Magazine: New magazines often have very stiff springs. Keeping them loaded for a few days or manually cycling rounds through them can break them in and improve reliability.
  5. Check for Binding/Clean Magazine: If the follower sticks, disassemble the magazine, clean it, and straighten the spring to ensure it is aligned vertically with the follower.
  6. "Wiggle" Test/Barricade Stop: If the magazine is loose, you might need to apply upward pressure on the magazine while feeding or use a shim to tighten the fit in the magwell.
If you are using a 3-lug action, it is noted that these magazines may require specific tuning.
 
Many thanks.
It’s definitely magazine sitting too low, and loose fitment. Not sure what the remedy is, whether it’s just the MDT mags don’t suit the KRG chassis well?
 
With out seeing what you are it’s hard
Will the magazine fit tight if you remove the action from the stock or is it loose no matter what
 
Yes, still loose. It’s not loose at the rear of the mag where the lip is, it’s the front of the mag that lifts up a lot
 
fordy1967 said:
Yes, still loose. It’s not loose at the rear of the mag where the lip is, it’s the front of the mag that lifts up a lot
Click to expand...
If you place a suitable washer at one end would it lift the clip end and make it more snug
Or remove some of the edge of the clip side of the magazine so it will sit closer at the other end
 
fordy1967 said:
Yes, still loose. It’s not loose at the rear of the mag where the lip is, it’s the front of the mag that lifts up a lot
Click to expand...
If you place a suitable washer at one end would it lift the clip end and make it more snug
Or remove some of the edge of the clip side so it will sit closer at the other end
 
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