Glock Marksman Barrel

[EMC45]

All, I just got a new G48 with the Marksman barrel...I have found it to be a pretty accurate barrel. Here's the rub.....It leads. I size my bullets to .358 and load them just like I have loaded them for other Glocks and my HP. No other gun leads like this. I load lead in my G36 with the polygonal rifling. It is always clean after shooting - as a matter of fact I put 93 rounds of Lee 230gr. TC through it yesterday and it looks shiny clean. The G48 got 100 TC 120gr Lee bullets and has a prominent lead wash through the barrel.

Any thoughts on this from the gun group here? I'm at a loss for this.

[LUCKYDAWG13]

My thought is try sizing down .357 or .356 I have G48 too just never shot cast in it yet but the Marksman barrel is supposed to be a tighter tolerance I had a XDm that would lead bad till i sized down

[EMC45]

I may try some .356. I thought that too.

[ioon44]

The first thing I do is slug the barrel to see what size bullet to start with and is the loading dies swaging the bullet down .

[fivegunner]

The first thing I do is slug the barrel to see what size bullet to start with and is the loading dies swaging the bullet down .

Yes Slug the barrel, that will tell you what to size the bullet

[W.R.Buchanan]

I would just powder coat the boolits and be done with it. That will solve your problem.

Randy

[Petrol & Powder]

Glock calls their new Gen 5 barrels, "Marksman Barrel". I have one and it shoots very well. But, I have not shot cast in it, so no help there.
The rifling looks to be a hybrid between the old polygonal rifling and traditional cut rifling. Sort of more prominent lands but with rounded grooves ? It's hard to explain. I don't think the type of rifling is to blame for the OP's leading issue.

My guess (and this is only a guess) is that Glock may be holding these newer barrels to slightly tighter tolerances. 0.358" may be a little fat for the new "Marksman Barrel", I really don't know.
I can say with some authority, 9mm barrel dimensions are all over the map. While .358" certainly works in some 9mm pistols, it doesn't work in all.

[GARD72977]

I have a G45. It seems to do fine with coated bullets.

[BNE]

I have the Glock 43X. Same size gun, but with .75” shorter barrel. I have only shot my powder coated Bullets through it. No leading issues. I size to 0.356”. Not sure if I have the perfect fit or coating makes up the difference. I agree to slug your barrel. That will give you another good piece of info.

BNE

[Bigslug]

Some of my studies on the matter - though not yet concluded: https://castboolits.gunloads.com/showthread.php?419722-The-Glock-Code-Cracked!-(Maybe-)

.356" seems to be the consistent 9mm bore diameter across what I've sampled so far (Glock old polygonal, new Marksman and others - Ruger, FEG, and Springfield), so at the moment anyway, I'm thinking starting with .357" for diameter is at least part of the answer.

I found nothing with bore slugs and pin gauges to suggest the diameters of Glocks - old or new - are any different than what's found across the 9mm spectrum. If there's anything peculiar to the throat or bore profile that might prevent proper sealing. . .that may be a field for additional study.

I'm running tumble-lubers, but have yet to find the ideal combination of variables to ensure totally clean, leading-free operation in Glocks or others. I've got to play with my TL methods and possibly try some of the same slugs run through a lube sizer, as well as play with hardness to see at what point the fouling goes away.

Based on previous 9mm struggles to avoid the brass sizing the bullets below optimum diameter on seating, I'm thinking I may be running too hard an alloy. Running a slightly fatter expander now, so I fear this is going to take some time consuming hard science with a hundred bullets of alloy A, a hundred of alloy B. . .

[Ia.redneck]

Great advice getting the boolit fit right. I've also helped some barrels by using JB Bore cleaner to smooth them up a little.

[EMC45]

I have yet to slug this barrel. I have slugged all my others in the past, however. I will say the Glock polygonal rifling I have shot lead out of (9MM, .40 cal. 10MM and .45 ACP) has never given a problem. For as much hoopla there is surrounding poly rifling and lead I have to admit I've never seen it. Years back my brother bought a G19 and we promptly put 100 rounds of the Lee 120gr. TC sized at .358 through it. A dry paper towel pushed down the bore on the plastic cleaning rod is all it took and the powder fouling was gone. No leading. Same for my G36.

I will push a box worth of bullets through the .356 sizer and see what I got and go from there. I normally have stuck with .358 since they shoot so well through everything else. Not every gun is the same though.........

[Cosmic_Charlie]

Does this marksman barrel have a generous throat? Just curious.

[EMC45]

All the research I've done says Glock tightened everything up - including the throat.

[Catshooter]

I've had Glocks that correct sizing didn't stop the leading. I went to water-dropping and that solved it. I was shooting WW+2% tin and they came out about 22 BHN.


Cat

[EMC45]

I shot 50 rounds of 120gr Lee TC sized to .356 over 3.7gr Bullseye. A lot better accuracy. Super tight groups. Still some leading when I got home I brushed it out with Hoppes and a brush. Not as bad as last time, but I shot 50 vs. 100 rounds. The group size is what really surprised me. It's a neat little gun and is pretty accurate.

[FergusonTO35]

May want to try giving those Lee slugs a dip in diluted LLA also. A little more lube on the surface really helps in my experience.

[Petander]

I just posted in another thread.

A new Glock 19 Gen 5 MOS.

300 rounds of .356" / 153 grn Cast RN Mihec PC:d. Nothing in the barrel. My old Tanfoglio load.

https://i.postimg.cc/hGykwft1/IMG-20231216-172747-538-3.jpg