Why Does SAAMI Spec Have Different .44Mag Bore Dia For Rifle And Handgun?

For a few years, fairly regularly, I'd read that some owners of .44mag rifles are unhappy with their accuracy. Yesterday, I saw a post where an owner slugged his rifle barrel and saw a difference in bore dia. compared to his handguns.

The answer came back that both guns are correct and that SAAMI has different specs for each. I just checked, and found these bore specs, Handgun .417, Long gun .424.

Seems that some factory rounds are somewhat loose fitting in some long gun barrels, requiring larger handloads.

I checked two other common pistol calibers also used for rifles, .357Mag and .45 Colt, and there is no separate rifle spec like there is for the .44mag.

Does anyone here know why these bores need to be different?

Try as I may, I cannot find any reference to SAAMI bore diameter specs. Perhaps someone can give me a reference. Cartridge and chamber specs, yes; bore specs, no. The only reference I can find is a listing of nominal bore diameters for various cartridges, and that says .44 Magnum is .430, with no distinction between the rifle and handgun. The reason for slugging a bore in the first place is that various manufacturers use different bore specs for all sorts of cartridges.

These are from SAAMI | Sporting Arms and Ammunition Manufacturers' Institute Handgun on Page 166, Rifle on Page 339

The bore and groove dim is at the upper right of both drawings.

I have to admit that surprises me.

OK, there's a clue is in the title of the drawings: VPI TEST BARREL. You'll note the inclusion of location of the pressure sensor. You'll also note on the rifling specs that the rifle has 12 grooves, the pistol 6 grooves. It would appear that the rifle test barrel is for Marlin micro-groove rifling, the pistol for conventional rifling.

With a specified groove diameter, bore diameter is going to vary depending upon depth of the rifling. Conventional rifling is deeper, so the bore diameter will be less.

That said, recall that test barrels are designed to create worst case scenarios FOR THE AMMO MANUFACTURERS from the variations that manufacturers are will create. Given various different rifling profiles, there may well be different pressure test barrels to suit the various/dominant rifling profiles for any given caliber.

Take note of the twist rate of the rifle. That is the biggest reason some .44 Mag rifles have accuracy issues. I would imagine it is compounded by loose bullet fit.

I have an early issue Ruger Deerstalker.The iron sighted groups aren't much smaller than my M29 using 240gr. ammo.

Use Internet Explorer for Saami

Saami Specs are set up to be viewed only with Internet Explorer. So I start out on Microsoft Edge, then hit the three dots on the upper right that pulls down a menu so you can switch to Internet Explorer.
What your really want is the cartridge and chamber drawing in the "Rifle" section which will be marked page 143. Just put the little hand on 44 Remington Magnum and click it, then you can view it or print it by printing the current page. Note that this is actually page 155 of the specs, there are several pages of introductory stuff.
Marlin must have been the first to submit the Saami spec and they were calling for the 12 groove shallow Micro-grooves with the 1 in 38 twist, hence the .424 bore,.431 groove with a plus .004" tolerance (that's right, you could have a .428 bore and .435 groove and just be at the edge of the tolerance). Marlin may have changed that later in their own internal processes, I'll check with Glen Fryxell. The Saami specs are voluntary of course. A manufacturer using conventional rifling would have a smaller bore.

"Saami Specs are set up to be viewed only with Internet Explorer. "

Not aware of that. Firefox and Opera work fine for me.

armprairie said:

Saami Specs are set up to be viewed only with Internet Explorer. So I start out on Microsoft Edge, then hit the three dots on the upper right that pulls down a menu so you can switch to Internet Explorer.
What your really want is the cartridge and chamber drawing in the "Rifle" section which will be marked page 143. Just put the little hand on 44 Remington Magnum and click it, then you can view it or print it by printing the current page. Note that this is actually page 155 of the specs, there are several pages of introductory stuff.
Marlin must have been the first to submit the Saami spec and they were calling for the 12 groove shallow Micro-grooves with the 1 in 38 twist, hence the .424 bore,.431 groove with a plus .004" tolerance (that's right, you could have a .428 bore and .435 groove and just be at the edge of the tolerance). Marlin may have changed that later in their own internal processes, I'll check with Glen Fryxell. The Saami specs are voluntary of course. A manufacturer using conventional rifling would have a smaller bore.

Click to expand...

I found the page you were talking about.

Since whenever that rifle spec above was submitted, I believe that Marlin went to "Ballard type" rifling in the .44 Magnum.

So if I understand you guys right, the same SAAMI bullets traveling down the two different bores diameters should react properly because of the different rifling designs.

So when these owners load a larger diameter bullet and get better accuracy in the rifle, it's not because of the larger bore, it's because of the design and twist of the rifling, and maybe some dimensional variation.

No wonder I see people questioning their rifle's accuracy. Seems unnecessarily complicated.

Thanks guys for making the effort to explain this art y'all are so good at.

WR Moore said:

Since whenever that rifle spec above was submitted, I believe that Marlin went to "Ballard type" rifling in the .44 Magnum.

Click to expand...

It says this on their site:

20” barrel with deep-cut Ballard-type rifling (6 grooves)

1:38” twist rate

Using some of what I just learned here I came across an article that covers this.

"Also in the 1960s, Marlin introduced the .44 Magnum to the Model 336. This rifle was fitted with Microgroove barrels, containing 12 grooves that were .062" wide and .0043" deep. Factory specs for the .44 Magnum barrels also called for a 1 in 38" twist, but that this time nominal groove diameter was to be held to .4315", and a bore diameter of .4230", so oversized cast bullets are once again called for."

Later in the article it says:

"As of fall of 2007, Marlin still makes a number of guns that have Microgroove barrels on them (according to the 2007 Marlin catalog posted on their website). All of their .22 LR and .22 Magnum rifles still have Microgroove barrels. The 336s in .30-30 and .35 Remington are still made with Microgroove barrels, however the stainless 336XLR in .30-30 and .35 Remington have Ballard rifled barrels. All of the big-bore Marlin leverguns (e.g. 444, 1895, etc.) are now fitted with Ballard rifled barrels (both blued and stainless guns), as are the 1894 and 1895 Cowboy models. Interestingly, in the 1894 series, the.44 Magnum and .357 Magnum guns are Ballard rifled, but the .32-20 1894CL and .41 Magnum 1894 FG are both fitted with Microgroove barrels."

So it seems they eliminated the Microgroove in 2007 for the .44 magnum caliber in question.

Thanks again guys, I wouldn't have found it without you.

I wonder if this need to use oversized cast bullets is mentioned in the owners manual, and how many frustrated factory ammo shooters this created.

It does cause a lot of frustration!

It certainly does cause a lot of frustration, not only in the .44, but in the .357 and .41. A friend of mine has one in .357 that will shoot jacketed just fine, but no good with lead unless he wants to keep one batch of bullets sized so large they won't even fit into the throats of his revolvers. His Winchester 94 handles both just fine. The newer Ballard rifling would probably work just fine with both. The bullet size does make a huge difference with the Marlin Micro-groove, as it does with the 30-30 from my experience, but moreso with the pistol calibers.
This is a real common discussion over on the cast bullet websites. Glad someone went to the trouble of quoting Glen Fryxell's comments on this.

armprairie said:

It certainly does cause a lot of frustration, not only in the .44, but in the .357 and .41. A friend of mine has one in .357 that will shoot jacketed just fine, but no good with lead unless he wants to keep one batch of bullets sized so large they won't even fit into the throats of his revolvers. His Winchester 94 handles both just fine. The newer Ballard rifling would probably work just fine with both. The bullet size does make a huge difference with the Marlin Micro-groove, as it does with the 30-30 from my experience, but moreso with the pistol calibers.
This is a real common discussion over on the cast bullet websites. Glad someone went to the trouble of quoting Glen Fryxell's comments on this.

Click to expand...

Don't recall seeing those other calibers causing people problems, only .44. Might be that more .357 shooters use jacketed. I'll keep it in mind though.

The early Marlin Model 1895 (the modern 1895) rifles in .45-70 had microgroove rifling. That was fine as long as jacketed bullets were used. But it was soon discovered that microgroove didn't work so well for lead bullets. I don't know how long it took, but Marlin did go back to Ballard rifling for the 1895. I once had an early 1895 and I can attest to that problem. It grouped well when I used jacketed bullets, but like a shotgun with lead bullets. I did come up with lead bullet loads which didn't group too badly, but still not so good. Surprisingly, that 1895 grouped better with lead bullets and black powder rather than with smokeless powder. I did a lot of load experimentation with that 1895 back in the early 1980s and kept records, but I have no idea where those records are today. Probably long gone.

bigwheelzip said:

Don't recall seeing those other calibers causing people problems, only .44. Might be that more .357 shooters use jacketed. I'll keep it in mind though.

Click to expand...

It has a lot to do with twist rates. 357 and 45 Colt rifles have the same twist as the handguns, usually 1:20. The 44 handgun is 1:20 while the rifle is 1:38.

I can cast bullets oversize to compensate for the oversize bore, but there is nothing I can do about the twist rate, short of rebarreling.

I gave my father in law a 1894 in 44 mag. Shot jacketed bullets fine. forget lead..was terrible. I also had a 1895 45-70 like DWalt had. Jacketed was fine. A friend??(I questioned that at the time) gave me 90 pounds of cast sized lubed bullets. Only one of the 6 different bullets shot worth a darn. The rest were almost as bad as long range buckshot groups. I sold that sucker and got the newer Cowboy model with Ballard rifling and it wil shoot almost any lead bullet well....But it does have a safety.