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5/35 SMc Loading Data Data and theory in this font is from By Smalley [Comments and data in italic font and brackets, as in this note, is from Mic McPherson] [This 5mm/35 SMc™ loading data and information is only preliminary in nature. Some of these loads may generate case ruining pressure. Start low and work up carefully watching for all recognized signs of excessive pressure – difficult extraction, excessively flattened primers, blanked or partially blanked primers, loose primer pockets after several reloading cycles, leaking primer pockets, etc. As of August 2005, a custom 5/35-chambered rifle built by Darrel Holland has already gotten two novice shooters into the Varmint Hunter’s 500-yard club! Precision gun maker George Myer is building several guns in this chambering. Experience with many propellants shows that SMc designs work with a wider burning rate range than one would expect – compared to conventional designs, these numbers are very forgiving. We have been able to obtain near normal results with ball-type propellants running the gamut from 2230 to W760 and with extruded propellants from H322 to VarGet (the latter is entirely too hard to use in a 20-caliber case, in my opinion). By has blown up many bullets with N540 loads so it is certainly capable of good velocity. There still exist many likely useful but untested propellants; however, I believe that we have looked at some of the best options – see data below. SMc case designs are unusually forgiving as to primer choice. I tested 5/35 loads with the 7½, WSR, 205M and BR-4 in one loading (Ramshot 1720, with the old 33-grain Hornady V-Max) with one seating depth. In that limited test BR-4s produced the smallest groups. 205Ms (205 Match) showed the best consistency and therefore have potential; however, 205Ms tend to blank (pierce) primers if the firing pin does not fit the bolt well and when one pushes the pressure too high. I was not concerned with reducing ballistic variation as all tested 5/35 loads are sufficiently consistent for shots beyond 400 yards! We have seen many loads generate single-digit standard deviations! Note: Usable capacity, loads and performance are similar between the 5mm/35 SMc and the 20 BR. The SMc has the significant advantage of a longer neck – usefully longer barrel life – and likely slightly less barrel heating due to superior trapping of unignited propellant within the case – owing to a superior shoulder design. The 20 BR is a very good, conventional, case design but has no advantage over the 5/35 and is likely to show reduced barrel life and increased barrel heating so is therefore less desirable. (Reforming 6mm BR cases for either design involves precisely the same amount of work – two simple necking steps.)] All my testing was done with moly coated bullets because I am lazy about cleaning. Mic says I load toward higher pressures than I should. Please start testing about one-grain lower! Some of this testing was done with a ¾-degree (included angle) leade before we gave up on it. Now we use standard benchrest leade of 1½-degrees (included angle). [Important Note: For loads using non-moly-plated bullets, reduce starting loads by an additional 1½-grains.] DATA: Likely maximum load charges, 30- and 32-grain bullets:
Likely Maximum Load charges, 35-grain bullets:
Likely Maximum Load charges, 39- and 40-grain bullets:
Mic likes TAC but I have not tried it. [I have also used the non-canister 1720 from Ramshot, which is between TAC and Big Game in burning speed, it works wonderfully if one does not mind swirl-charging – I have a swirl-charging funnel that attaches to my powder measure so this is very easy for me to do.] My favorite powder for this cartridge is Benchmark, it burns clean! [I agree, this is by far the cleanest of all tested propellants (if it only filled the case better!) I have fired almost three hundred rounds without cleaning and without any evidence of a fouling-related reduction in accuracy! Subsequent testing proves that H322 is just as clean and gives about 20 fps higher velocity and is at least as temperature stable — I now use H322 exclusively for loads with 32-grain bullets.] H335 is the most flexible but it is [entirely!] too dirty [for extended shooting strings at vermin without cleaning. As far as twist rate goes, I think I can recommend 16-inch for 30-grain Berger bullets at velocities of 4600 ft/sec or higher. [Recent testing proved that this twist would not work with the 32-grain Sierra or Hornady at about 2500 feet elevations. It works great with those bullets at Cortez (6300 feet elevation). It also worked with the shorter Berger 30-grain bullet at around 2000 feet elevation but might not work at sea level.] 14-inch for 32- and 35-grain bullets at 4400 to 4600 ft/sec. 12-inch for 39- and 40-grain bullets. [The 14-inch twist did not work with 39s and 40s at 4500 feet elevation.] 12-inch seems to be best overall [Further testing proved that the 12-twist disintegrates 32-grain V-Max and BlitzKing bullets when loaded at full 5/35 velocity, a 13-twist might work for those.] [The 12-inch twist is hard on the current crop of lighter bullets when those are driven at maximum velocity, I would be happy to try a 13-inch twist if I wanted to use heavier bullets. However, because I have no interest in those, I would prefer a 15-inch twist. In comparison testing between Pac-Nor barrels I saw no velocity difference between the 12-inch and the 16-inch twist when launching light bullets at maximum velocity — the same loads worked about the same in both barrels when I tested the 32-grain B-Tip, which works perfectly in the 12-twist.] Berger bullets are most accurate but are relatively] delicate, I can blow them up if I push them too hard. Have not tried 50-grain Bergers, they require 9-inch twist but Walt is using these in benchrest with some success in a version of the PPC case. I have not had good success with Sierras to date, I think these may have growing pains [conversely, I have had very good results, different production lots perhaps?]. Hornady bullets are OK but not as accurate as the Bergers are. Historically Norma cases has been better dimensionally, and with regard to neck and shoulder annealing, but Lapua cases will withstand somewhat more pressure. [With my help, Norma solved this and the case head hardness deficit of Norma cases, compared to Lapua cases no longer exists.] Norma was supposed to ship the first acceptance lot of properly headstamped brass in July but we have not received it yet. [Those are now promised near the end of September 2005.] Barrel cutoff test results were performed with two bullets, 32- and 40-grain Hornady bullets with 31.5-grains H322 and 32-grains Benchmark, respectively, at starting velocities of 4399 and 4190 fps, respectively. This starting with a factory 26-inch Savage, 12-inch twist barrel:
*Anomalous reading, not explained by standard deviations or the 40-degree warmer day, I apologize for the terse way I write, just cannot help being an engineer. [And I apologize for my verbosity, I have learned this through years of difficult retraining, in an effort to make my writing easier to follow!] Good luck and better shooting By Smalley [Mic McPherson] |
