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Identifying bedding issues

30 Jul 2023
@ 11:36 pm (GMT)

Rob Bird

Hi all. I've been working with my 7mm Practical build this summer. Had it done by a very good smith recommended by Nathan. Rem 700 action, blueprinted, Krieger 5R barrel. The rifle I used came with a very nice custom walnut stock, looks a lot like a McMillan Game Warden with a cheek piece. Pillar bedded and then full length bedded. Came out pretty good. Had to do some slight relieving to get the action to go in and out of the bedding easily. Barrel is fully floated to the knox.

I've done a number of different loads out of it and always manage to get at least one flier on a 5 shot group. 4-5 minutes of cooling between shots. Barrel never feels more than just warm. I was getting what looked like double-grouping on some loads, though after doing a little relieving, that seems to have gone away. I've tried 162 gr and 180 gr ELD-M, along with 150 gr Federal Terminal Ascent. All behave about the same.

My question to you all is if you have any tips for identifying possible trouble areas in the bedding. Because I figure either I have a bedding issue or a barrel issue. I use Winchester primers and haven't tried anything different. Not sure if that could account for any of the issues.


31 Jul 2023
@ 12:00 am (GMT)

Rob Bird

Re: Identifying bedding issues
One thing I just checked that I should have verified before is that the neck on fired brass is .315" with .028" of thickness. That means that I'm at .287" ID on a fired case. A bit small, no?

I'm going to turn a few necks and see what happens.
31 Jul 2023
@ 07:17 am (GMT)

Nathan Foster

Re: Identifying bedding issues
Hi Rob, regarding the bedding, try the 1 o'clock test, maybe use a pencil line on the barrel. Check for mag box pinching and check the fit of the underside. That should pretty much cover the basics.

if the barrel is still relatively new then keep an eye on the copper fouling - both extremes. If fouling is very heavy, then the bore will need to be run in a bit more.

If the bore does not produce any fouling whatsoever, this can also be a problem (details on this in both the Rifles and Accurizing books). Of the latter, observe the accuracy, velocity and ES of the first 3 to 4 shots on a cold clean bore versus the next 3 to 4 shots with the bore coated in powder / graphite residue. If the accuracy, velocity, ES go out of whack during shots 4 to 7 etc, then the finish may be too high. Besides limiting cleaning, I don't actually have a fix for this sorry. It is something I have tried to address in the book series but is a difficult topic because in order to prevent problems, customers have to be educated first as a means to change their demands of manufacturers. This cannot be changed at the manufacturer level because if manufacturers take the lead on this, customers will go back to complaining about having to take time breaking in their barrels. Sorry - quite a large topic on its own but having read the series, I am sure you have the jist of this. In any case, the chrony, paper results and in some instances primer pockets (spikes) can help you find the evidence you need to draw conclusions.

Yes, .002" is a bit close. Close tolerances are required for rimless handgun but can (not always though) create pressure / harmonic issues in a bottle neck rifle cartridge depending on potency / pressures etc. If you want to, try turning say 6 cases and see how these go with a couple of different loads (e.g, over a previous sweet spot such as 71.5gr powder and then 72gr). A half moon skim off the case should be enough to get you another thou or two. No need to get too heavy about it.

As you can imagine, a tight neck may produce results that look similar to the issues of a high finish bore. The trick will be to isolate these variables.
02 Aug 2023
@ 11:17 pm (GMT)

Rob Bird

Re: Identifying bedding issues
Thank you for the response! I forgot to mention that I have verified that the mag box is fully clear (after removing material from it). I have not penciled the barrel but cannot feel any movement on the one o'clock test.

I did two 5 shot groups with turned necks, but did not think to try different loads on the same bullet. I actually did a 162 gr ELDM and a 180 gr ELDM. The effect on both was what I've been experiencing - one flyer per group with the rest around .5-.6 MOA (which may be my personal minimum average size - I've never consistently shot any better than a .5 MOA average).

I will have to get back to you on accuracy/ES on the first 3 to 4 shots. I always do 2 foulers that are fire-forming loads in order to bring more cases into the rotation. These are on a clean, cold bore and use cheap 150 gr pulled bullets and, incidentally, often are touching on paper. On the last visit, my first shot for record was the flyer, with the other 4 grouped. Then, with the second load of 180s, the first 4 were the group and the last was the flyer.
03 Aug 2023
@ 08:06 am (GMT)

Nathan Foster

Re: Identifying bedding issues
Try if you can to monitor the muzzle, looking across it in good light. A magnifying glass helps a lot. You are going to need this info in order to determine how to move ahead.

Bright orange fouling after shooting session - needs to be stripped away / more time to break in.

No fouling - drop the cleaning regime to the bare minimum and allow fouling to build (protective coating only / avoid gun solvents).

Trigger about 1.5lb for this type of sub minute / sub half minute precision shooting.

Keep an eye on ammo concentricity.

Extra heavy or extra light neck tension can muck things up a bit. Heavy tension may be a problem if you chose a Redding neck bushing for a thin walled case - but then used a heavy walled case (your neck turned cases will likely have less tension next time around).

Otherwise and as suggested, monitor your loads over the chrony (set it well away from you) vs the target. The two together can help tell you a bit more about what might be going on inside the bore in conjunction with visual observations of the muzzle.

Little steps.

04 Aug 2023
@ 12:06 am (GMT)

Rob Bird

Re: Identifying bedding issues
Thank you! For neck sizing, I've actually been using a .307 bushing for unturned cases. The .311 one did not get me there...I could easily slide bullets in by hand. And for turned cases I'm using a .304. all instances, I use an expander mandrel sized at .284, so I am at about 1 to 2 thou in tension. Too little? If I don't expand, in either case (turned or unturned), I'm at approximately .279-280 ID, assuming 1 to 2 thou of spring-back after sizing (unturned necks are 28 thou and turned are 26 thou). I have not fired any that I did not expand.

For a chrony, I've been using a Labradar I got a screaming deal on. My Jewell trigger is quite light. As for fouling, you may have hit on it. After the other day's session of 12 shots, there is light copper on two of the lands near the muzzle. A bore scope shows only light white powdery deposits throughout the barrel and only minor streaks of orange.

For loads, I've mainly done the 162 gr ELD-M. I use standard Winchester primers because that's what I am able to get. My understanding is that they are hotter than Federals. My top load is 77 grains of H1000 that gives me an average velocity of just a shade under...3300 fps! Perhaps that gives a clue.

04 Aug 2023
@ 07:30 am (GMT)

Nathan Foster

Re: Identifying bedding issues
Hi Rob, about .002" tension is good. The following may or may not apply so please ignore if I am covering ground you have been over.

Be careful about arriving at an ideal neck tension via a tight bushing followed by reliance on a flare / expander button to achieve the desired tension. If the case is not entirely aligned during neck expansion, the process may muck up concentricity which will cause fliers.

I understand that bushings are not exactly pocket change and that it can add to costs when trialing bushings, but this may be the key to issues (a concentricity gauge would say one way or another).

Minor streaks of orange is about perfect. If its quite light, it may pay to leave it in there and keep shooting. Most lubes / protectants (including CRC) will remove some copper no matter how much you try and keep it in there so perhaps swab the bore with whatever you are using, then dry swab prior to the next range session and see how those streaks look at the muzzle.

If you do need to remove the copper (to clean up that muzzle section), try a minimal approach, going at it gently.

Later, if you need to polish the throat - and you find that the bore is producing very little copper - apply solvent to the throat section only, clean it, then polish, then use alcohol or some such to get the solvent out of the bore, neutralizing it immediately so that the extent of the bore is unaffected by this cleaning process.

An aside for other readers:

It gets a bit trickier with suppressed rifles. Sometimes one may need to retain copper plus carbon in the bore to keep the rifle shooting well (generally if the bore has a very high finish). In this instance, it is important to keep the bore coated in a protectant to prevent corrosion during storage. But it is just as important to keep the chamber clean from compacted carbon (see book series / see also last section of youtube video - is it me or is it my rifle). Besides cleaning the neck and throat section of the suppressed rifle, the bore will also need an occasional deep clean using a bronze brush and solvent. Determining when this needs to be done again depends on the internal finish of the bore. If it has a very high finish and is a mongrel for the first dozen shots, it stands to reason that you don't want to have to go through a half pack of ammo just to get it shooting straight each time you use it. All this stuff can be worked out during the initial phase of breaking it in, getting to know its behavior. The key is to understand consequences of both action and inaction (see book series for more information).

04 Aug 2023
@ 08:25 am (GMT)

Rob Bird

Re: Identifying bedding issues
Thanks again. I do check concentricity, though not always religiously. I try to be careful about not forcing the expander but rather to let it gently go in to allow the case to self-align, but I do get that there are no guides to keep it perfectly straight as there are in a neck bushing die.

The cool thing about not fully cleaning the bore is that now, I can just go straight to my load and see if my first cold bore shot always goes where intended.

09 Aug 2023
@ 10:20 am (GMT)

Rob Bird

Re: Identifying bedding issues
Did 5 shots of 162gr ELD-M over 77 grains of H1000. All rounds had 2 thou or less runout on the bullet. Group was .860". Average velocity 3279 fps, ES 68.

Group size may just be me, though in the same session, I put 5 rounds inside 1.5" at 100 yards with my K31 with stock open sights. It could be that I'm not managing recoil aggressively enough. I do grip the forend tightly, but maybe I need to force it into my shoulder harder. And I must admit that I've not been using a sling.

In terms of the rifle itself, the only other thing that I can think of is that sometimes it's hard to close the bolt since I had the mini m16 extractor installed. On 1 in 3 rounds, I have to force the bolt handle down. I am having it feed from the magazine.


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