As the weather is rubbish here, I spent a bit of time in the man cave this afternoon to measure some bits / do some testing which may help. The original BSA springs I have for the 45" guns, (originals are stamped on the ends), both single and twin sets are 0.136" gauge wire x 33 coils if single, 17 coils (left and right wound) if twins. They are a quite stiff temper and I have read that the twin springs on the larger guns were introduced as they were getting breakages back then (pre ww1) in the large single springs, and the effect of fitting twins reduced the recoil somewhat and gave a slightly smoother shooting gun, the latter I have found to be the case personally. This was in the improved model gun era, ie. pre 1914...I am not sure what happened after WW1, I have understood that later 20's / 30's standards had large single springs from new, so maybe they had changed the tempering process / learnt something in between
Anyway, I did some chrono testing on a late standard with 4 types of pellets, you will notice how much better the wasps are in consistency than the domes' or H+N's, and the gun shoots the most quietly and smoothly with these, it is noticeably more noisy and harsh with the FTT's, with the superdomes being in between. The superfields were aweful, dropping the power down to the mid 9's and I only fired two!
Back to springs...I quickly pulled the gun apart and had a look, it is well shot in, and the piston moves easily in the cylinder under finger pressure with the slightest drag, the spring fitted is an Airsporter one (0.127" wire x 33 coils), so the same length as an original BSA one, but thinner wire gauge. These are good units as long as you fit either a quality pattern, or preferably an original...there was a guy selling genuine N.O.S. Airsporter springs on the Bay, they were only a tenner or so and I put a heads up on here a while back, they are top quality and worth stocking up as many replacements are simply not as good!
The next photo shows 3 springs,
The top one is a N.O.S. BSA Airsporter which measures 10 1/4" overall, with a wire gauge of 0.127" x 33 coils.
The second set are a set of pattern twin springs, in 0.134" wire x 17 coils, these are 10 1/8" long, and were removed from a gun as it was very harsh and over the limit!
The third set are a set of original BSA twin springs, these are 0.136" wire x 17 coils , a stiff temper, and are 9 1/4" inches overall..this gives minimal preload, and these springs give mid 11's in energy and are very smooth in operation.
You will notice the striking difference in the length between the pattern and genuine twin sets, due to the more open winding...I have several other BSA twin springs, and they are all shorter than these patterns, and more interestingly, if you measure between the gaps of the coils on both the genuine BSA Airsporter, and the genuine BSA twin sets I have, the variation is a minimal plus or minus 0.002"...ie very accurately wound...the patterns vary by up to 0.030" between coils, this must have some effect I would imagine (but don't know what) or maybe it matters not a jot, but they are not as accurately made as the genuine ones!
Anyway, guns do vary but most people highly rate the wasp .22 pellets in these, and they always fetch good money when they appear for sale, the superdomes and the FTT's are both very good accuracy wise, especially at longer ranges, but many people who have never fired the period pellets in their prewar .22's would be surprised at the effect they have on the firing cycle, they just seem to suit most guns better and they shoot noticeably more quietly.
So...decent airsporter spring and superdomes seem to work well in this gun, so you are on the right track with the pellet choice you have. Lakey's point about cleaning was something I forgot to mention, in the past I have posted about results I have had after cleaning what initially looked like a smoothbore, it was so full of crud!
Eddie adds in a different thread:
I recently acquired a little used Model B (43" gun) which shoots very well (in the low 700's with hobby pellets) and the spring was a flatwound original BSA.
Spring gauge is 0.160" x 0.082 Flatwire x 40 coils. The preload is 2" which sounds a lot, but the spring (as are most flat / oval types encountered) has a fairly soft temper / feel, so assembly is easy with little effort required, in comparison with the JK springs with a similar preload length, which are brutes!...
I have had good results in the past with flat springs from T W Chambers, the part number being MS016 which is a 40 coil as per the model B above.
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