Cause of barrel leading

[kevin c]

So I had nasty leading towards the muzzle along with keyholing and horrible accuracy in a new 9mm pistol barrel, using an alloy, bullet style, HiTek coating and load that had worked just fine in my other Glocks (confirmed by subsequently shooting the same lot of ammo through my other guns without any such problems).

So far I’ve found two potential barrel issues.

The first is just plain poor barrel machining. All my other barrels, both OFM and aftermarket, with polygonal or standard lands and grooves rifling, had a smooth, even mirror like internal finish. This barrel (reportedly a Glock factory “Marksman Barrel” from a third party vendor) has machine marks on the whole length of every land and groove, along with what to my inexperienced eye look like chatter marks as well.

The other is that I just did a preliminary slugging of the barrel in question, along with an after market Glock barrel with standard rifling (a BarSto) and an OFM polygonal barrel off a G34. The groove to groove diameter on the BarSto was 0.356” and the valley to valley diameter of the G34 was the same. The suspect barrel had a groove to groove diameter of 0.359”!!!

This is the first time I’ve encountered this type of problem. I will double and triple check the bore slugging, but are there other things I should consider? If not, is the 0.002” misfit (I cast 0.358” and size to 0.357” after coating) the most likely culprit?

And what to do? I’m a bit doubtful that I can coat up another thousandth with HiTek, and really don’t want to tinker with my 95-3-2 alloy and casting technique in order to cast “fat” (I’ve premade what I figure to be several years ‘ supply). Should I be in the market for a new barrel?

[shooting on a shoestring]

Yes.

[shooting on a shoestring]

Shooting a boolit that is smaller than barrel groove diameter is the main ingredient for barrel leading.

You have to fit the boolits to the barrel for reciprocators. For revolvers you size the chamber exits to groove diameter and then fit the boolits to chamber exits.

The boolits have to be at minimum (means will sometimes work good enough) the same size as the groove diameter to a maximum of about 0.002” bigger than barrel groove diameter. This is the Golden Rule of shooting cast boolits.

The way we cranky old guys would solve your problem is to keep casting with the mold that works for your other 9 mm’s and get a new mold to fit the fatter barrel. There’s a good chance if you keep doing this hobby you will have another gun (or 2 or 3 or…) that will need the fatter boolit. Also, there’s a real good chance the fatter boolit will work great in some (maybe all) of your previous 9mm’s. So getting the new mold in a different nose shape, or weight or different configuration would let you tinker with new loads in your old guns too.

The cheapest way out of your dilemma is probably just trading off the fat barreled gun to someone who shoots jacketed bullets. It’ll work fine for that. Or getting a new barrel. But be sure to know what the new barrel measures at before you buy it.

It’s not uncommon to see 9mm barrels have groove diameters anywhere from 0.354”-0.359” in real life.

[shooting on a shoestring]

There was a former member here with the handle “Beagle”. He solved situations like yours by using small slivers of aluminum duct tape applied to the mating face of one mold halve. The aluminum adhesive duct tape is about 0.002 to 0.003” thick. This would let the mold cast very slightly oblong boolits, but of an average fatter diameter. Works amazingly well! That idea is referred to as “Beagling a mold”.

[shooting on a shoestring]

Concerning chatter marks in the rifling grooves, that’s fairly common. Could certainly be contributing factor but, I own several pretty bad looking, chattered bores that shoot clean. So that is not a certain doom.

A chattered barrel could be helped by firelapping the sharp peaks off the chatter marks. Give it a try.

[Gtek]

Fit is King!

[Dusty Bannister]

Have you tried a larger diameter bullet with a soft wax based bullet lube like the NRA 50/50? Have you done anything to condition the barrel before shooting the lubed bullets? It sounds like either the alloy or the lube has failed. Since the alloy works in other arms, more than likely the type of bullet lubricant is failing.

[BK7saum]

I have to wonder if you will ever get this barrel to shoot without leading. If the chamber is in spec, you are probably going to have trouble getting a fat 0.359 (minimum) or a 0.360/0.361 bullet to chamber just due to the width of the case mouth (bullet dia + case wall thicknessx2).

Based upon the poor internal finish and oversize bore, I would try ro get a refund on this problem barrel. With the poor finish and so far from the spec on your others, IF you get it to work, you are most likely going to have to load ammo specifically for this barrel.

And do not even attempt to use the Lee FCD to get your boolits to chamber. They would be so fat that you would be sizing them inside the case, leading to loose undersize boolits, possible bullet setback and high pressure.

Life is too short to deal with a problem barrel or gun unless it is a unique collector piece.

I sold a 1911 9mm that I bought new just because it had a tight chamber (most likely match spec) Factory ammo and brass chambered fine, but a good percentage of reloads needed to be bulge busted to chamber. I started down that road and then decided it wasn't worth it to me to go to the trouble to bulge bust brass for one firearm.

[405grain]

Sounds like some third party vendor bought factory reject barrels at a discount, and is reselling them to an unsuspecting public. If I were an unscrupulous snake oil salesman I would use words like "Marksman" or "Tactical" on the junk I was shilling. Fastest, best solution is to toss that defective barrel and replace it with one of known good quality.

[PJEagle]

I traveled down the same path a couple of years ago. By the time you expand the brass enough to accommodate the larger boolit; the rounds won't chamber. It's time for a new barrel. Sending the barrel to DougGuy won't help in this case; he tried to help mine. He does great work on everything else, but an oversized 9MM barrel needs to end up in the scrap heap.

[gwpercle]

Sounds like some third party vendor bought factory reject barrels at a discount, and is reselling them to an unsuspecting public. If I were an unscrupulous snake oil salesman I would use words like "Marksman" or "Tactical" on the junk I was shilling. Fastest, best solution is to toss that defective barrel and replace it with one of known good quality.

Agree 100% ...

Loading lead in a 9mm Luger is hard enough ...

Loading Lead in a Wonky (rough machine & chatter marks ) barrel is going to be next to impossible ...

Life's too short ... cut your losses on that barrel and buy a known quality barrel .

You will be a lot happier !
Gary

[kevin c]

Well I repeated the bore slugging in all three barrels, (twice more in the problem barrel), all with basically the same numbers.

I don’t think it’s the alloy or coating, since I don’t get leading in my longer G34 barrels shooting the exact same lot of bullets in the same load. I considered the possibility of the boolit being swaged down, but while I am using a different HS of brass that might be thicker, I use a custom M style die so I doubt that. Still I’ll be thorough and check the coating, pull and mic a few boolits, and maybe even cast and try some boolits in Hardball alloy instead of the 95-3-2. But the two findings already known make me think that a different barrel might be my best option.

Thanks for all the suggestions!

[DougGuy]

You can't "fit" to that barrel b/c of boolit size limitations of the chamber. That barrel is unserviceable. Replace the barrel.

[kevin c]

DougGuy:

The more I think about it, the more I believe you and the others recommending a new barrel are right. I’ve always wanted to try a KKM barrel so, while it’s a month’s wait, I might be giving them a call.

I might be pm’ing you as well, as the BarSto 9mm won’t “plunk and turn”, otherwise I might have used that instead of this problem barrel (though my impression is that the polygonal barrels get me a few more fps, an advantage in my gun games, and thought that was what I was getting, though it turned out to be standard rifling. The crown and the rifling make me conclude it was a Marksman barrel, but that’s my own assumption; it could be the barrel was not of Glock manufacture at all).

Well it was cheap; the KKM will cost twice as much, and now I know why. Live and learn.

[mnewcomb59]

If you're getting a KKM make sure to get a slower twist. I believe KKM makes 9mm barrels in any twist you want up to 30". 9mm with 10" twist is WAY overspun for a cast bullet. 10" twist could shoot a subsonic 300 gr without tumbling. WAY too much twist.

If you get a 16-30" twist barrel it will shoot any lead with no problems. If you get a 10" twist you are stuck with hard lead only. With a 10" twist the bullet will skid on the riflings instead of biting and riding and sealing. 10" twist is the one and only reason that 9mm is hard to load cast bullets. If you're getting a custom barrel for lead bullets definitely get a better twist rate.

Edit: I checked their website and saw this: "Our standard twist rate is 1:16 for ALL makes and models. It is the only twist rate we offer for Glock and M&P.

If you are looking for a different barrel model, we have options from 1:10 – 1:34. Just tell us your preferred twist rate in the optional note section of the Checkout screen. There is no extra charge and we read every note prior to production. "

The slower twist would make cast HPs shoot like a dream. With my 10" twist 9mms with soft-ish lead and HP boolits I pretty much top out at 1050 fps before skidding and leading in the corners of the lands and grooves.

[jsizemore]

Is your gun made in Austria or USA? Even though Glock says they are the same, the tolerances are "looser" on the USA guns.

[kevin c]

jsizemore:

The frame is probably US Glock manufacture, though I don’t have it in front of me to inspect. The slide is aftermarket (basically I got one pre milled for a dot sight) with a mix of Glock OFM and aftermarket internals.

I should probably pop the barrel off one of my all factory original G17s and install it in my Frankenstein to see if the hodgepodge is inherently capable of reasonable accuracy apart from the one barrel’s fit and leading issues.