9mm Pf Anomaly

[Suches]

I'd appreciate some wisdom from those more knowledgable. I'm loading a 147gr Montana Gold CMJ over 3.2gr Titegroup, 1.130 OAL. It reliably makes 880-885 fps, or 130ish PF, out of my G34. I recently chrono'ed it out of my full-sized Springfield 1911 9mm, and got wide variations of 805-830 fps, way below IPSC and IDPA legal. The 1911 has a Bar-Sto barrel, and is dead accurate and shoots beautifully, so I assume the bullet isn't rattling around in there. For grins I loaded some West Coast plated 147s, and guess what, back to the 880-890 range, but accuracy is to hell, including a few keyholes. I loaded various OALs with no significant variation. I"ve emailed Bar-Sto a couple of times, but they haven't had a chance to get back to me. Any ideas?

Thanks!

[Harmon]

new barrel?

probably lot sharper rifling than the glock, slowing the MG bullet down and cutting the plating off the plated bullet.

solution?

shoot it more!..load(or buy) some 115 grain ammo. run a couple K rounds down the barrel...it will likely slick up and start shooting faster...if not you may just have to load 2 different kinds of ammo for the two pistols.

[LJE]

It reliably makes 880-885 fps, or 130ish PF, out of my G34. I recently chrono'ed it out of my full-sized Springfield 1911 9mm, and got wide variations of 805-830 fps, way below IPSC and IDPA legal. The 1911 has a Bar-Sto barrel, and is dead accurate and shoots beautifully, so I assume the bullet isn't rattling around in there.

The Glock barrel has hexagonal rifling, and will have higher velocities than a barrel with conventional rifling. I recently experienced the same when developing 9mm major loads using MG 124 JHP for my KKM barrel G34. Using the same load, the Glock barrel displayed velocities 30 to 40 fps faster than the KKM, and also 70 to 80 fps faster than a 6" Storm Lake barrel. The hexagonal rifling seems to create less friction on the bullet.

Larry

Edited October 24, 2005 by LJE

[Vlad]

Also the length of the chambering and the distance between the chamber and the lands could make a difference. I use a similar load in my CZ (Zero bullets instead of MG) and I get 129PF.

Edited October 24, 2005 by Vlad

[Harmon]

if that were the case why would one bullet go fast and the other not in the 1911, whereas they both shot fast in the glock...

[LJE]

if that were the case why would one bullet go fast and the other not in the 1911, whereas they both shot fast in the glock...

Put a hexagonal rifled barrel in the 1911, and now you can do a valid test with that gun. We have shot loads through different Glock barrels and other aftermarket barrels, and the Glock hexagonal rifled barrel is always faster, even though it sometimes was shorter than the other barrels we tried. Perhaps another way of experimenting would be to compare the velocities of a conventional rifled barrel and an H&K hexagonal rifled barrel, provided the barrel are the same length.

Also, I would want to shoot that West Coast plated bullet load in the Glock and see if it is even faster than the MG load in the Glock. I would bet that it is. I believe the plated bullet will squeeze into the rifling easier than the jacketed MG bullet, thus producing higher velocities in each gun.

Edited October 25, 2005 by LJE

[warpspeed]

I've never been able to get any accuracy at all with plated bullets. And I'm not the only one.

[LPatterson]

The Glock barrel has hexagonal rifling, and will have higher velocities than a barrel with conventional rifling. I recently experienced the same when developing 9mm major loads using MG 124 JHP for my KKM barrel G34. Using the same load, the Glock barrel displayed velocities 30 to 40 fps faster than the KKM, and also 70 to 80 fps faster than a 6" Storm Lake barrel. The hexagonal rifling seems to create less friction on the bullet.

Larry

A Glock does not have rifling per se but hexagonal flats (octagonal in a 21) therefore there is less resistance than convential lands & grooves which cut into the bullet causing drag. This is why lead bullets are not recommended because they shed in the corners of the flats causing a decreased bore diameter.

One hypothesis as to why plated bullets lose accuracy is that they are being deformed by the barrel flats crushing the plating into the lead in an off balance condition. In most rifled barrels the lands are greater than the thickness of the plating thereby imprinting the rifling into the lead.

[gm iprod]

Glocks have a 'polyagonal' barrel.

Some guns display a wide variation of velocity for no apparant reason.

Glocks do usually give slightly higher velocities than traditional rifled barrels. Even at the same length.

25fps extreme spread is good, on any load. The Glock barrel 34 barrel is slightly longer. But 80fps or 105 is a sizable increase over the Springfield, if the barrels are the same length.

I have experienced in rifles as much as 100fps difference between a load in two otherwise identical guns. So go figure.

Find the most accurate bullet / powder combo for each individual gun and go with that. You sometimes get lucky and can use the same load across a wide range of guns, but not often.