Low energy double-based powders

[Catch-22]

Hi,

 

So I think most of us know that it's generally best to use a 'single base' cool burning powder, rather than the high energy 'double-based' powders, if you want to preserve as much barrel life as possible. Many thanks Laurie for all the articles and posts on the subject!

 

However, it looks like I may get best performance with the heavy 300g bullets in my 338 Norma Mag using Ramshot Magnum - a powder a lot of people in the States say works very well.

Looking at some data sheets, and a helpful forum thread, it seems not all 'double-base' powders have to have the highest energy rating of all powders. E.g. Ramshot Magnum is somewhere around 3,775joules, where as VN560 is around 4,000joules.

https://thefiringline.com/forums/showthread.php?t=545581

 

My question is, does anyone know if by using a lower energy rated 'double-base' (like Ramshot Magnum), is it still going to be a barrel burner?

We know the likes of RE-17 and VN550/60 are barrel burners but they have very high energy ratings (4,000joules or more), but if by using one that has a lower energy rating (Ramshot Mag at 3,775joules), should I expect better barrel life? Ramshot Mag has a very similar energy rating to VN150, a relatively cool burning 'single base' powder, so does it mean lower energy 'double-base' powders are ok?

 

Many thanks!

[Catch-22]

Does anyone know?

[Laurie]

I think the answer to that question is more likely opinions rather than facts. All one can say on the subject is that studies were done by the US military in the early days of the 7.62 that compared barrel life between Olin Corporation (now General Dynamics, St. Marks Powder Co., Florida) ball powders against traditional Dupont Corporation manufactured IMR extruded types. Olin ball powders were (and still are) all double-based as are all spherical / ball grades including Ramshot powders; the IMR products were all single-based at that time. (Not anymore - the 4 Enduron grades have small nitroglycerin components.)

 

Anyway, back in 19 oatcake, no appreciable difference in barrel life was found between the two types at standard pressure levels.

 

The pros for ball types became excellent charge density, long storage life, and crucially more accurate mechanical metering in ammunition factories giving small charge weight variations and hence MAPs but just as important gas port pressures in automatic weapons.

 

The downsides were greater temperature sensitivity (for any propellant that incorporates nitroglycerin however it gets there) and in the case of older ball types that had a large percentage of non inflammables in the mix - nearly 10% by weight in some grades - were dirty burners needing more frequent and thorough cleaning. (The M16A1 experience in Vietnam was salutary. The AR-15/M16 and the original 5.56mm cartridge had been developed with IMR extruded grades and then the US DoD decided without reference to rifle designer Gene Stoner and manufacturer Colt to adopt an Olin ball powder as a matter of general procurement policy. There were two results - changes in pressure curves that increased cyclic rates and wear and tear on recoil buffers and action parts; a large increase in fouling in the gas system and bolt group assembly. The latter allied to the in-theatre tropical climate and an extremely unwise manufacturer's sales policy that said these weapons needed no, or at most, minimal cleaning, saw stoppages rise to disastrous levels until proper cleaning equipment was issued and training put in place.)

 

Recent developments have mitigated both ball powder downsides, and PB Clermont which makes Ramshot grades is now probably the planet's leader in ball powder R&D making its products much less temperature affected and 'cleaner' and very highly regarded in military circles. Ball powder R&D investment by all parties over recent years has been very heavy as the US Army in particular has become increasingly demanding, and also as a result of extensive operations in Iraq and Afghanistan with their huge temperature swings and soaring summer daytime heat.

 

Now, that leaves a third group - the extruded 'high-energy' types - Viht N500 series, nearly all Alliant Re extruded grades, around half Nitrochemie's RS rifle grades. They start as single-based extruded kernels and undergo a nitroglycerin infusion process before modifiers and deterrents are added. Some of these are literally and figuratively 'hot' especially Viht N530 and N540, but many such types such as most Nitrochemie powders and Alliant Re grades actually have lower specific energy values than single-based ADI/Hodgdon H4895 and VarGet.

 

Separate from that, Nitrochemie high-energy grades all have the company's patented EI deterrent infusion process that really stretches the initial slow burn period out - in terms of both elapsed time after primer ignition and bullet movement down the barrel. This allied to 4,000 KJ/Kg energy gives considerably enhanced MVs in appropriate applications - eg + 150-200 fps for 105s in the 6XC and for heavy bullets in 284 Win from RS60 / Alliant Re17. However, we now know that to make use of that performance potential is barrel-killing. It's likely the combination of heat, peak pressure, and crucially the extended duration of the peak values for the first pair thanks to EI technology that cause the problems.

 

What happens if you use these powders, but don't run them at loads that give any higher MVs than Viht N100 series or RS non-high-energy / EI such as RS50 and 62? Good question .... and I don't have an answer! In theory, they'll produce the MV/ME value at lower pressures than single-based alternatives, but peak pressures lasting longer. Irrespective of what they might do or not do to barrel throats, some grades have acquired an unfortunate reputation for temperature sensitivity - Re17 in the USA and the US DoD changed the specification of the M118LR 7.62mm 175gn sniper round from Alliant Re15 to IMR-4064 after pressure problems arose in Middle East summer temperatures.

 

So, 338 Norma Magnum and Ramshot Magnum? You should be OK in barrel life . There is another factor to consider. Whilst one might wish to run this and similar powders at modest pressures, sometimes (oftentimes?) ball grades don't let you. ie they provide inconsistent results and large ES/SD values until they get pretty close to peak pressures. (Also, their optimum pressure operating window is relatively narrow between too low / inconsistent and too high with a rapid spike into excessive pressures.) My personal experience with Ramshot has been good, but you do have to watch this factor closely in some applications with some powders, eg Hodgdon CFE223 which is an excellent performer but has a rather narrow operating band IME. As I increasingly avoid things with large cases and heavy powder charges these days (and I mean well before we get to the size of this big bugger!) I've never had the opportunity to try Magnum with anything .... but good luck. (And tell us if the barrel packs up after 50 rounds - Nah, only kidding )

[Catch-22]

Ha - thanks for the insightful feedback Laurie!

 

I'll give RSM a go (in addition to N165) as the original cartridge designer, Jimmy Sloan, said it was the optimum powder for it. Plus it's available here too.

 

Reading various forums, Sloan and Dave Tooley (vast experience with big 338s and has many years experience with the 338NM and 338L) state they're easily getting around 3500/4000 rounds from their 338NMs. I think a big factor is not trying to hot rod it, same with any cartridge really.

Many in the US simply chase those max volicities, trying to push the large 300grainers at 2850 and more - that's way beyond what was originally conceived. To do this, many of these velocity chasers are burning huge quantities of N560, N570 and Re-33 (RS80) and theyre suffering short barrel life as a consequence.

 

I just think RSM will perform better than N165 with those heavy 300s (I reckon N165 will be stellar with the 250s but too fast for the 300s) and I think N170 will be just too bulky, will not fully burn and won't attain optimum velocity.

 

Once the rifle's complete and I've tried RSM, I'll report back.

 

Many thanks again!