Firelapping The .45 ACP
Four Gun Test
J. Marshall Stanton
Conventional wisdom in regard to the time-tested 1911 auto pistol platform to attain enhanced accuracy focuses traditionally upon either tightening tolerances of the gun, or advanced techniques in handload tuning.
This test approaches the subject with a little different direction and emphasis. We began the project with four different firearms, three in model 1911 persuasion and one Glock Model 30. All four guns were tested with two separate .45 ACP loads, both before, and after firelapping, to evaluate what effect the lapping process produced on each of the four test subjects.
This article is NOT intended to be a review of the various firearms used in this exercise, but rather merely observations made during the testing, and the various aspects and peculiarities of each gun as they pertained to this investigation.
The Test Guns
The four .45 ACP test subjects were as follows:
- Taurus PT 1911 AR: This was a NIB firearm prior to firing for these tests, it is the newer AR variant of Taurus’ PT 1911 model in stainless steel. Sights are OEM installed Heine three-dot sights.
- Norinco 1911A1: This 20+ year old pistol has seen lots of rounds down-range! It has an old Colt 70 series barrel and a couple of other functional upgrades, but has never been “accurized” as such. Sights are OEM installed three-dot style in basic G.I. configuration.
- Ruger SR1911: This gun also was NIB before shooting for this evaluation, it too is stainless steel. Sights are OEM installed Novak three-dot sights.
- Glock 30: This gun has seen a fair amount of use, and has had previous trigger work done. Too, a new Lone Wolf threaded barrel was installed just for this test and was unfired when we started this project. Sights are OEM installed, typical Glock style, white dot-front and white-outlined rear configuration.
No attempt was made to break in these weapons prior to testing, and only two magazines of ammo were fired through each gun before shooting for groups on paper.
The ammunition used for this test was all loaded using a Hornady Lock-N-Load AP Progressive press and the Hornady powder measure furnished with the press. Dies were an RCBS carbide three dies set. All ammunition was loaded without changing anything in the loading regimen, except for the seating stem on the seating die to adjust proper bullet seating depth of the two respective bullets.
The two loads used throughout the testing were as follows:
- Hornady .451”-230g FMJ-RN/5.0g Bullseye/WLPP/C.O.L. 1.250”
- BTB .452”-225g FNB BB/5.0g Bullseye/WLPP/C.O.L 1.168”
No attempt was made to tailor a load to any individual gun, and the load selected is merely one that has proven to be predictable in a variety of .45 ACP chambered weapons, and is middle of the road both in velocity and pressure.
All test firing was done at the BTB Shooting Range, off a sandbag rest at 25 measured yards. Shooting was conducted over a four day period of favorable, clear, sunny weather with no wind and temperatures in the low 70’s.
Each weapon was fired seven rounds per target, and a minimum of three targets per type of ammo, both pre and post lapping, and in many cases many, more targets than that, fired with each gun with the different ammo if obvious human error in shooting results was observed. In all, several hundreds of rounds were fired in obtaining test results.
All targets were fired over a new RCBS Ammomaster Chronograph at a distance of 15 measured feet from the muzzle to record velocities.
Group Measurement Techniques
As already pointed out, all targets were fired with seven rounds each, without exception. As is the case with many autoloading pistols, two of our test weapons showed a distinct tendency to throw the first round out of the subsequent group, therefor, the one single round farthest out of the group was discarded, and all measurements based upon the remaining six rounds per target, center-to-center. All targets, regardless of weapon used, were measured in this manner.
In the above chart, group sizes are listed as “Huge” for the Glock 30 fitted with the Lone Wolf barrel. After multiple targets with both loads at 25 yards, we could never get more than four rounds out of seven to hit a 8.5”x 11” target, and gave up trying!
In all firearms, test firing was first done with the jacketed Hornady FMJ’s, then the weapons were cleaned, followed by shooting the BTB FNB’s, then the firearms were cleaned once again.
Evaluation of Pre-Lapping Data
Upon disassembly for cleaning after shooting alloy bullets in the pre-lapping tests, barrel leading ranged from nothing, to absolutely HORRIFIC! In searching for a means of quantifying the degree of leading, the barrels were cleaned of lead via an undersized bore brush wrapped with copper scouring pad as a lead remover. The barrels were individually cleaned over a large piece of butcher paper, and the lead collected on the paper was poured onto the pan of a digital powder scale and weighed.
Lead deposits from all barrels were processed in a like manner, cleaning with the lead remover, then weighing the removed lead.
After the final pre-lapping barrel cleaning, each bore was slugged, using #8 Oval Egg Sinkers, and the groove diameter measured, as seen below. (Bumping Up Oval Egg Sinkers for this application.)
We slugged the Taurus PT 1911 AR twice, simply because of the large groove diameter, just to double check that the measurements were correct.
Lapping The Barrels
After testing all four guns with both loads, and evaluation of those results it was time to lap the barrels, and get on with the project.
Processing a hundred lapping bullets, embedding the abrasive into the bearing surfaces took over two hours! (Perhaps the biggest mistake made in firelapping is not investing enough time rolling abrasive into the bullets.) All lapping bullets prepared using Beartooth Bullets Lapping Kit.
Once the bullets were prepared for the lapping project they were placed in a plastic container until loaded.
Lap loads consisted of fired cases, unsized, decapped and reprimed, with the case mouth slightly flared to accept the lapping bullets (Which measured .453” when lapping compound was fully embedded into the bearing surfaces.), and a charge of 1.8 grains of Bullseye powder. (It is ESSENTIAL to use only BB-gun velocity loads for lapping!) We used up some odd, left over Fiocchi large pistol primers in this lapping project.
Each of the test guns was firelapped with a total of 25 rounds per weapon. The chamber was cleaned between each shot to remove any residue from blowback around the case. (.410 shotgun swabs, bent at 90 degrees just below the threaded portion and screwed onto a short handgun cleaning rod work great for this purpose!) Barrels were thoroughly cleaned between every five rounds.
Finally, all four test barrels were polished using 100 brisk strokes with a polishing-bob charged with abrasive, as is detailed in the Beartooth Bullets Technical Guide, and then each cleaned thoroughly once again.
Prior to reassembling the test guns, a repeat slugging of the bores, using expanded #8 oval egg sinkers and meticulous measuring revealed no measurable or discernible change in nominal groove diameter of any of the newly lapped barrels as compared to the pre-lapping dimensions.
A strict and uniform barrel break-in regimen (again as detailed in the Technical Guide) was followed for each firearm prior to testing resumption, and shooting for groups post-lapping.
Post-Lapping Shooting Trials & Evaluation
Again, all shooting for groups was conducted over an RCBS Ammomaster Chronograph, from sandbags on a solid bench at the BTB Shooting Range. Temperature was 74 degrees, clear, sunny, and not a breath of breeze. All post-lapping tests were completed in one sitting.
Ammunition employed originated from remaining stocks of the two loads fired in pre-lapping tests, and every effort was made to duplicate the conditions under which the original tests were fired. In both the pre and post lapping tests lighting conditions under the covered shooting bench were ideal for sight acquisition and shooting.
The data in the table below was calculated and measured with the exact same methodology employed in the pre-lapping data evaluation.
Surprisingly, the Taurus PT 1911 AR shot the BTB 452”- 225g FNB BB surprisingly well, considering the .453” groove diameter of this pistol!
The Glock 30 with the Lone Wolf barrel at least settled down enough post-lapping to get all seven rounds on a target at 25 yards! Too, it showed some promise with the cast BTB 452”- 225g FNB BB bullet. This was the last firearm that was fired on the post-lapping test strings, and it’s possible that after 300+ rounds of .45 ACP that I simply wasn’t shooting my best. None-the-less, the barrel at least shoots more predictably than it did prior to firelapping.
The Ruger SR1911, after lapping shows potential to be a really fine shooting weapon. The vertical stringing was probably shooter induced on the right hand target.
Some Interesting Observations
After shooting all four of the test weapons with 35 rounds of the BTB 452”- 225g FNB BB ammo, the weapons were field stripped, and the bores examined, and cleaned with the lead remover over butcher paper as was done prior to lapping. The only barrel that showed any leading at all, was the Taurus PT 1911 AR, not surprisingly, since it has a .453” groove diameter, and we were pushing .452” diameter bullets down the barrel. HOWEVER, the astonishing thing was that in this particular barrel the leading was only in the first 1/8” of the barrel, at the throat, and the remainder of the bore was bright and shiny. Now, there wasn’t enough lead in the bore to even register on the PACT digital scale! Neither was there in any of the tested barrels after being lapped!
Too, in each and every barrel there was a velocity gain. Modest increase? Yes, but apparent none-the-less, and achieved with identical loads and guns across the board. This increase in velocity came both with jacketed and cast bullets.
Accuracy improved in all four guns with both jacketed and cast bullet loads. Interestingly, each and every gun pre-lapping had a preference for jacketed bullets, and shot the best groups during testing with the Hornady .451”- 230g-FMJ-RN bullet with the test loads. However, in post-lapping testing, all four guns showed a marked preference for the cast bullet load using the BTB .425”- 225g-FNB BB projectile! Yet, that improvement also came with an increase in the accuracy of the jacketed bullet load as well. In no case did accuracy deteriorate in any gun with either load.
Conclusions and Final Thoughts
While this test is by no means a comprehensive and exhaustive test of all the variants of a .45 ACP available, the data gathered and compiled through this exercise does indicate that a little judicious firelapping did have a profound positive effect upon the weapons tested.
Interesting too, bullet seating depth, bullet selection, bullet diameter, powder selection and charge weights were never a part of this test, in tuning a load to one of the weapons. In fact, an arbitrary book load was employed using two different bullets, and very satisfactory post lapping results happened. One must also keep in mind that this ammo was loaded in mixed, once-fired brass of various manufacturers, and some even nickel plated.
It is very possible that fresh, matched, factory loads would yield even better post-lapping accuracy results.
Also, shooter fatigue in the post-lapping tests surely hampered achieving full accuracy potential realized from the lapping process in these guns.
The project was enjoyable, and instructive, and we hope that our reader finds it interesting and useful as well.
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