The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

Today I finished off a Bearing surface comparator. This was a trial project that Mark (Spud) and I had been talking about,

6mmBR sum it's purpose up very nicely:

Why Does Bearing Surface Length Matter?
A bullet's bearing surface is the full diameter section that actually contacts barrel rifling. A longer bearing surface creates more friction which can lead to higher pressures. Also, when seating bullets close to the lands, large variances in BS can mean that some bullets engage the rifling while others do not, even with identical cartridge OAL. This can cause shot-to-shot pressure variances, increase Extreme Velocity Spreads (ES), and degrade accuracy, particularly at long range. Consistent bearing surface lengths help optimize ES and accuracy.

The hard part is turning the internal diameter of the comparator surfaces top and bottom, the slightest slip and it they are oversize and scrap for this size bullet. I ended up building the top section in stainless and I am tempted to turn a stainless bush insert for the bottom section as it is easier to machine in some ways and means the bush can be swapped out for different sizes so you could measure say 6.5mm/7mm & .308

Very well done,I bought mine and sure it did help with the new Sierra 2156 once sorted
we got the very best group.
sincerely
Fiippo

Looking good there Dave i didnt realise it was coming on a wooden plinth with built in electrics but hey good thinking there.How stable do you find it on the granite, would a bigger foot print bit be better for the next project ( have i meantioned that yet) oops .

Stainless insert added.

spud wrote:Looking good there Dave i didnt realise it was coming on a wooden plinth with built in electrics but hey good thinking there.How stable do you find it on the granite, would a bigger foot print bit be better for the next project ( have i meantioned that yet) oops .

Stability seems OK however I have not glued the mast in yet, I will do that last thing tonight. It should be quite stable as it is.

You may not be able to see but it is sporting Stainless comparators top and bottom, the last top I turned was on a cold day, today it was hot and the bullets were sliding through, I can only assume it expanded slightly.. The stainless ones are not quite as open as the aluminium ones but are a better job I think.

What is the next project?

i am after a better /bigger bottom for my shell holder for my whidden pointing system


like you commented on on abnother forum the other day ;0

Stainless would be nice then, I built my prototype out of aluminium to prove it works, I will build a couple in stainless

thanks buddy

You would love having access to our scrap skip its full of stainless and all sorts of other exotic metals.

Alpha1 wrote:You would love having access to our scrap skip its full of stainless and all sorts of other exotic metals.

I tell everyone to look out for any scraps, anything from 6mm to 50mm diameter and any length any material.

I assume your scrap bin is not local...