1972 Small Pack

I recently got this small pack from one of our members here. I thought it was a P51 small pack at first glance but it turns out that it is dated 1972...styled like the P51 pack...and has OD green plastic buckles. Another feature is the wide loops on the back that are folded over and sewn to create belt loops. Also note the phenolic resin ends on the straps. The construction is exactly like the P51 pack except for the alterations mentioned.

I have a few other pieces that look like P51 web but have the plastic buckles and post-P51 dates. Does anyone know why this web variant was made? And what is the official pattern designation?

...and I thought P37 web was frustrating

Well, turns out that I had the answer here all along. After thumbing through Jack Summers book "Tangled Web" this pack turns out to be a modified P51 pack to adapt to P64 web. Also states that it was a failure.

It is not 64 Pattern.  It is late production 51 Pattern.  The later 51 Pattern had the plastic buckles.  Note the wide straps on the back of the bag for attaching to L straps.
I thought at first it was 64 Pattern as I also have one of these and also have Summer's book.  But, I don't think any L straps were made for 64 pattern webbing.  And besides, if you are going to use this bag with 64 Pattern webbing, why not just use the original 51 Pattern bag with the original L straps?
Ian

To me it looks like the pack was designed to hang from the belt since the straps are made into loops.

Hi,
First, to make the loops you need some buckles.  There are no buckles on the bag and there are no buckles on the belt.  Second, where would you attach this bag to the 64 Pattern belt?  After adding all the other 64 Pattern items to the belt, there would be no room left over to add a bag.  At the very least, it would have to be mounted on the right side and forward.  Not a good place to have a large bag.  And, what would be the advantage be to adding a bag this large to the belt?  The weight of the bag plus contents would make the belt sag to one side.  It would be better to carry the bag on your back, as mentioned in Summers although this was a failure.
As I mentioned before, I also have the radio carrier with nylon buckles, and have also seen another version of the carrier that I have, NOS in a plastic bag with a NSN.  As well, the last version of the 51 Pattern belt also had a nylon buckle.  
Regards,
Ian